StumbleUpon is on a roll. As of August 2011, the U.S.'s biggest serendipity engine drove drive half of all social media traffic, surpassing Facebook, the social network that formerly held that bragging right.

Today StumbleUpon announces a complete overhaul of its platform and logo, as it aims to make the site more visually oriented and simpler to use. Now the user profile makes visible all connections, comments, interests, channels, likes, shares, inbox and history. All of a user's thumbs-up are visible through the profile. The new StumbleUpon also features channels, which are essentially sponsored Twitter-like accounts that a user can follow. Plus, the layout looks a lot more like its social network cousin, Pinterest.

StumbleUpon is the inverse of a Google Web search. Instead of typing in a keyword and searching for relevant links within that search, StumbleUpon asks the user to define the parameters by selecting a topic, and then voting the content up or down. Using the Explore Box, users can type in an interest that's more specific than one of the many comprehensive topic options. It gives a list of related interests, which broadens the breadth of topics to stumble. Over time the user develops an interest profile specific to them.

The new channels, which allow users to follow content from sites (The Atlantic Wire), celebrities (Tom Hanks, Jim Carrey) and brands (Gilt, Campbell's Kitchen, Audi), mirror more of a Twitter model. For celebrities and brands, this form of advertising is more subtle and, as a result, less intrusive. The new site also makes it easier to keep track of all the pages, photos and videos that a user has liked in the past; the old version only gave users easy access to posts they had shared.

Earlier this year StumbleUpon launched the Explore Box, a tool that's useful for helping Stumblers find topics related to a single topic. If a user is trying to find topics related to "Sleeping Beauty," for example, type in "Sleeping Beauty" and then a list of related interests pop up, such as "Sleeping Beauty Castle," "The Sleeping Beauty," "Sleeping Bag," "Sleeping Bear Dunes National Lakeshore" (OK, the last two were a bit odd, but that's alright). The Explore Box also suggests things it thinks you might like based on the original interest; in this instance, the suggestions are "animation," "France" and "Paris." In the new relaunch, the Explore Box is integrated right into the user experience.

StumbleUpon is a prime example of the read/write web. Why? Because the user literally writes their own "taste graph" by signaling to the service what interests they want to follow. In the e-commerce space, EBay acquired recommendation engine Hunch to do just that - serve up more relevant content to users.

StumbleUpon launched an iPad app back in July. In November, StumbleUpon came to the Kindle Fire.

How do you like the new StumbleUpon? Tell us about it in the comments below.