Summary: Web 2.0 is everyday, non-technical people using the Web to enhance their lives and businesses. The fact that so many people are now creating and building on the Web is what the '2.0' signifies.
Tim Bray dislikes the Web 2.0 meme, but mainly because it isn't technically version 2.0. With all due respect, this totally misses the point. Web 2.0 is about building new things on top of the Web - the 'Web as Platform' definition I wrote about recently.
It's an era of unprecedented construction on the Web and this has generated a lot of excitement and optimism. As Danny Ayers pointed out when he referenced Ian Davis' words: "Web 2.0 is an attitude not a technology".
Web 2.0 is not necessarily version 2 of the Web. The "2.0" part just happens to be a witty software reference signifying that it's a new world of Web opportunity. As Tim O'Reilly said in his post responding to Bray's: "...there's something qualitatively different about today's web."
Tim O'Reilly summed it up:
"Web 2.0 is the era when people have come to realize that it's not the software that enables the web that matters so much as the services that are delivered over the web. [...] The net has replaced the PC as the platform that matters, just as the PC replaced the mainframe and minicomputer."
So much is being built on top of this Web platform nowadays: new media such as blogging and podcasting, old media is moving to the Web, music (e.g. Webjay, iTunes), education, shopping (e.g. Amazon, eBay), marketing, banking, law, government - you name it, it's being built out on the Web.
I think Tom Foremski captured this point in his recent post, when he said:
"The new dotcoms are not technology companies, necessarily, but they are all "technology enabled" companies."
And that's what Web 2.0 means to me - everyday, non-technical people using Web technologies to enhance their own lives and businesses. The Web is an infrastructure, a foundation. What we create and build on the Web is what Web 2.0 is all about.