The Facebook client looks pretty similar to the typical Xbox Experience interface, with individual sidescrolling windows that might actually be a little tedious to trawl through. It'll also support Facebook Connect, which will let you upload, for example, in-game screenshots to your Facebook profile in real-time.
Xbox Live will also get Twitter, though we don't know much about it yet—looks like it's presented in one big feed, unlike Facebook, which is great. We'll keep you updated as we learn more. And for more ongoing info, head over to our liveblog.