I've had quite a bit of trouble figuring out what to do with some of the new social networking tools. I joined Facebook and Orkut at more or less the same time and for a while, I found Orkut easier to use. The problem with Facebook was that I was being inundated with application requests. Orkut didn't send me quite so many and it also integrated better with Google's set of apps.
Now however, I find that I'm leaning more towards Facebook. There are a number of reasons for this but the Blackberry interface and the greater popularity of Facebook certainly play a major role. I've quickly learned to completely ignore all of those application requests, pokes and other things but respond to requests for friends. Why? Well, I'm not into popularity contests but once you've added a friend, it's easier to find them if you want to talk later. Interestingly enough, I've found that a lot of people on Facebook don't actively check their messages - or maybe they just don't want to talk to me :-).
The thing that really changed my mind though, was the availability of some decent Facebook apps.
This is a book database where you can flag books that you've read, books that you'd like to read and books that you own. You can also give books ratings or reviews. This app basically puts you in touch with other people who liked the same books or who are reading the same book as you. I'd love to see more of this type of app - iMovie, iMusic anyone? There's bound to be something out there that does those jobs too. I'm looking at flickster, but it doesn't seem to be suitable so far.
Delicious, Digg and Stumbleupon
Now these add a lot of value since they expose your social bookmarks. I'm seriously considering specialising on these sites - ie: Deciding that Digg is only for my Computing news, StumbleUpon is only for Entertainment etc.. This would enable me to separate my list of bookmarks out into interest groups.