Facebook - The blockbuster seqel to all the geeky prequels! To paraphrase Tim Bray, I've seen this movie before. Only it's different this time. Unlike UUCP email, profs email, Nortel's Cocos, BBSes, Usenet, The Source, Compuserve, The Well, etc non geeky people of all ages are using Facebook to privately and semi-privately blog, share interests and email each other. Which I think is great! And I love that Facebook is becoming a platform.
But until you can get all your stuff (your status messages, your private messages, your wall posts, your events, your profile information, etc) out like you can get all your photos and all the associated metadata out of flickr using its APIs, I would be careful.
Just like everything else on the Internet, if it's not on a domain you own or control then it could be shut down and removed at any time without any prior notice.
In other words have fun with facebook but recognize that's the stuff on there is ephemeral and ethereal and mostly invisible to Google; if you want something permanent that the world can see whether or not they belong to Facebook, stick it up on a website or blog or wiki or other web app with permanent public URLs on your own domain.