In 2006, I think one of the most interesting developments in the online world was the convergence of blogger culture with social networking culture. Sites like Vox proved that social networks could successfully cater to grownups and bloggy-types, while blogs and social news platforms made efforts to beef up user profiles and social networking features such as friending, in-site mail, and media (pics, videos, audio, and text) sharing. One of my favorite social networking sites, MyBlogLog, is a stripped down social network that serves as a powerful networking and profiling tool for bloggers.
This year, I think there's going to be a lot of action in combining the immersive virtual world of MMOs (massive multiplayer online games) with advanced social networking features. Or, 2D-meets-3D if you like. TechCrunch's review of Kaneva showcases a good example, "a new social network that extends the concept of MySpace into a virtual world."
While Second Life has received quite a lot of buzz, a fair criticism is that people don't have a lot to do there. New MMOs will have a focus, even if it is to extend the hang out/check out bands/check out each other culture that thrives at massively popular social networking hubs such as MySpace. But I think that the online gaming world, more than anything, will incorporate web-based social networking features that support and extend existing game communities.