We hear a lot about digg, Slashdot and del.icio.us as traffic drivers for media websites and blogs. But one site that doesn't get enough props in this regard is StumbleUpon. In our recent Social Bookmarking Faceoff, we noted that StumbleUpon has the largest user base with 1,271,345 users. Its main rival in the space, del.icio.us, recently announced it had reached 1 million users.

StumbleUpon is basically a browser plugin which makes it very easy to submit and vote on websites. Simply download the plugin (Firefox or IE) and then click the "I like it!" icon to 'stumble' a webpage. Once a link has been submitted, it can propagate out to the large community of SU users in a very viral way.

Neil Patel, who has given me a lot of excellent advice about website optimization, recently wrote a post entitled How to get StumbledUpon. It's a great introduction to StumbleUpon and a must-read. In fact, subscribe to Neil's blog if this kind of thing interests you.

I can attest to the power of StumbleUpon - our most popular post over the past couple of months (according to my Google Analytics service) has been Top 10 Firefox Web 2.0 Add-ons. Usually our top posts are ones that have had the fortune to be Slashdotted or dugg. But this one got neither. Instead, 27% of its traffic was driven by StumbleUpon and 14% by del.icio.us. And the flow from StumbleUpon continues. I have to admit though that it's one of only a few R/WW posts to have been stumbled in a big way, so like digg and Slashdot it's not something publishers can expect on a regular basis.

StumbleUpon is yet another example of a Web-based community that has gained a significant user base in a seemingly short period of time. Check it out!