Music has been a huge part of the Web since the days when Geocities-hosted fan sites offered Nirvana MIDI files and 15-second clips of songs in WAV format. A decade ago, we saw the rise and fall of Napster, the remnants of which were recently sold yet again. From the ashes of Napster rose a new era of digital music, fueled in large part by the iPod and iTunes Music Store. The traditional structures of the music industry may never return to what they once were, and that's okay. Today we have access to more music than ever before and the tools for creating it are available to anyone who can afford a laptop.

Music is still a huge - and growing - part of the Web today. This year, we watched a number of trends unfold in the digital music space. Picking the five most significant was no easy task, but we manage to narrow it down. This space is still evolving, and we can only imagine how it will look another decade from now.

1. Music Moves Toward the Cloud

Buzz about "the cloud" in general has been building up for a few years now, but 2011 was the year that we saw our music collections begin to make their way toward Web-based repositories. First, there was the rise of all-you-can-stream music services like Rdio and Mog. That particular space was lit afire by the July U.S. launch of Spotify, which did not go unnoticed by its competitors, most of whom dropped their entry level price tags down to zero in order to keep up.

With these services, consumers move from playing MP3s on their hard drives to streaming tracks from the cloud, whether at their desktop or from their smartphones and tablets. In the case of Spotify, that cloud-based library of millions of tracks can even be merged with one's own local collection, providing a theoretically infinite library of music.

This year, we also saw the emergence of cloud music lockers. This model is a bit different from the streaming services in that it takes a person's existing collection and allows them to store it online for playback from any connected device. Amazon launched their Cloud Drive in late March, having already operated their own MP3 store for some time. The service allows music fans to upload and store their collections to Amazon's servers for streaming later.

Amazon's model is quite similar to the one offered by Google about eight months later when it publicly launched Google Music. The new initiative, which was first unveiled at Google I/O in May, took the cloud music locker concept the company originally built and added a digital music store on top of it, putting the service in direct competition with Amazon Cloud Drive.

Not to be left out of the cloud music game, Apple unveiled iTunes Match alongside iOS 5 and iCloud in June. Ten years after the company began revolutionizing digital music with the iPod, Apple decided to place a big bet on the idea that the cloud is where people will store their ever-expanding music collection in the future. Like Amazon and Google's solutions, iTunes Match enables access to one's collection across devices. Crucially, Apple's offering does not support streaming, but rather requires listeners to download tracks locally.

2. Online Music Gets More Social (or Annoying)

For as long as there have been Web music services, there have been attempts to bolt on social networking features. Some, like the Ping feature in iTunes, have fallen flat. Pandora has managed to become a relatively successful service without baking in very many social features at all. By comparison, Last.fm and Rdio are way more social.

As popular as it is in Europe and now the U.S., Spotify never had any ground-breaking social features of its own; Just the ability to share playlists and tracks over Twitter and Facebook and plug into other services like Last.fm. That all changed at the f8 developer conference in September when Spotify became one of a number of music services to get tight integration with Facebook.

Rather than try and take on Google, Amazon and Apple and smaller players in the music space, Facebook decided to partner with the likes of Mog, Rdio and Spotify to advance it's so-called "frictionless sharing" philosophy. By linking their Facebook account with any one of these services, users can automatically share every single track they listen to with their Facebook friends and start amassing aggregate monthly data about their listening habits on their Facebook profile.

The partnership has helped fuel enormous growth for Spotify and delighted some users, but not everybody is thrilled with the concept. CNet's Molly Wood wrote a biting critique of Facebook's new approach to sharing, and our own Marshall Kirkpatrick weighed in with a thoughtful critical analysis. ReadWriteWeb founder Richard MacManus had some concerns about it as well, but thinks Facebook is simply redefining sharing, rather than flat-out ruining it. Scott M. Fulton III reminded everybody that these features require users to opt-in, so avoiding the discomfort is as easy as doing nothing. If you've already connected Facebook and Spotify, but have had a change of heart, you can always turn the integration off.

Love it or hate the execution of it, Facebook's integration with music services is just the beginning of a more social experience when it comes to listening to and discovering music online.

3. Recommendation Evolves: Man vs. Machine

Digital music recommendation engines are nothing new. Pandora and Last.fm have provided listeners with algorithmically-determined suggestions for years. In 2011, as new music services cropped up left and right and the selection of available music continued to expand, listeners still found themselves with a thirst for solid recommendations for what to listen to next. Pandora, which filed for a $100 million IPO in February, continued to serve as an attractive Web radio option, with its powerful recommendation engine fueled by the Music Genome Project.

Even though it's overshadowed by the newer, all-you-can-stream music services, Last.fm still boasts a robust community and its music recommendation algorithm is often used by other apps (including Spotify), from which users can "scrobble" their music, creating a detailed profile of listening habits that can be used to discover similar artists.

A music recommendation system many have used, often without knowing it, is The Echo Nest. Their platform powers dozens of music apps with over 5 billion data points about music and various associations between different artists, albums and songs. To date, the Echo Nest Platform has indexed over 30 million songs, far more than Pandora.

As powerful as these machine-driven recommendation engines can be, there's still something to be said for human curation. For evidence of this, look no further than the popularity of apps like Shuffler.fm, a service that turns human-edited music blogs across the Internet into dynamic, genre-based radio stations. It takes a step away from the algorithm in favor of tastemakers, kind of like in the old days. Shufflr.fm received heaps of praise from the tech press over the summer and recently launched its iPad app, making unique music discovery experience portable.

4. Group Listening: Turntable.fm and Beyond

The value of this human touch in digital music curation was also seen in the rise of group-listening apps in 2011. The biggest and most buzz-worthy was Turntable.fm.

When the creators of mobile barcode scanning app Stickybits decide to pivot, as they say, to an entirely new type of mobile application, they didn't expect it to blow up quite the way it did. Turntable.fm, their virtual group-listening and DJ'ing Web app, became wildly popular and sparked several copycat sites, including one that was a near total rip-off of the original.

Turntable.fm allows users to get together in a virtual room and take turns playing DJ for one another, using music stored on their computer's hard drive. In September, the company brought this group listening experience to the mobile space when it launched an app for iPhone and iPad.

5. Music Creation Goes Mobile

It wasn't just music consumption that got a big boost in 2011. Creating it is now easier than ever, thanks to a growing array of digital tools.

Mobile apps geared toward creating music started appearing shortly after the launch of the iTunes App Store in 2008. As platforms like iOS and Android have grown more capable, so too have these kinds of applications. There's no shortage of apps that synthesize real instruments, and even ones that let you record your own samples, make beats and create songs from scratch.

In 2011, we saw Apple roll several of these concepts into one when it launched Garage Band for iPad, and then scaled it down for the iPhone and iPod Touch. It's not the first music recording and sequencing mobile app to appear, but for the price tag ($4.99), it's easily the most powerful. Garage Band for iOS includes dozens of synthesized instruments, which can often be pretty expensive when purchased as stand-alone apps. It also has several "smart" instruments for the less musically inclined.

Like its desktop counterpart, the core function of this app is to record and sequence multiple tracks of music. Using external accessories, one can even record vocals and guitars. Garage Band for iOS and apps like it provide an early glimpse of what's possible on tablets and smartphones, two categories of devices that are still relatively young.

It was a good year for SoundCloud, a social audio-hosting site that has grown quite popular among amateur and professional musicians alike. Big labels and known acts are using SoundCloud to post and promote music, while smaller artists and laptop hobbyists are finding audiences there as well. Think of it as sort of a YouTube for audio.

Like so many other popular Web services, SoundCloud pushed further into the mobile space this year, launching apps for iPhone, Android and iPad, among others. Users can not only use the service's mobile apps to stream and comment on music, but they can also record and post their own tracks right from the app.