Social bookmarking was one of those hot areas for a while back in 2006, as Del.icio.us and StumbleUpon exploded into popularity. Clones began to pop up everywhere, but few have managed to gain much ground.

That makes Diigo, a newer social bookmarker aimed toward information gathering that I reviewed last year, sound like something of a throwback. However, Diigo is releasing a new version today, and says it has a small but growing group of devotees.

Diigo is distinguished by its highlighting capabilities, which allow users to go through a page and mark certain portions. Users can also leave comments on pages, made visible by a Diigo plug-in available for most browsers.

That makes it great for research, but Diigo seems to be aiming at more of a mass audience with a set of new social networking and recommendation tools. Users can now join groups, send messages to each other and follow what friends are doing. Recommendations are provided based on your own bookmarking and existing tags and groups are available to search through, which can help new, friend-less users get started.

Diigo’s CEO, Wade Ren, told me that the service is getting some attention as a group research tool for people like teachers and marketers. It’s now somewhere north of 100,000 users.

Interestingly, Ren points out Delicious as the only competitor to his service that’s still innovating. However, it looks like traffic to Delicious is falling off, while StumbleUpon has spiked upward according to Alexa, Compete and Quantcast (click through for the charts). That may mean that the average user is actually interested in a less full-featured service.

Around the corner is Delicious 2.0 (coverage on that from TechCrunch), so we’ll soon have a chance to see.

diigo.JPG