I just downloaded it today, and I'm pretty impressed.
For those of you who don't know what it is, its a Chrome-based web browser that incorporates Facebook and Twitter in little sidebars. You can use Facebook chat, update your status, and browse your news feed. I don't really know what it does for Twitter because I don't use it, but I would imagine it you can "tweet" or whatever it is you kids do these days.
Clearly, if you aren't into the whole social networking thing, it isn't for you, but if you like Facebook, its worth checking out.