i'm on all 3! sad I know. Twitter i only joined a couple of days ago, its crap, im not going to bother with it.
Facebook I was really into at the start, keeping everything updated and poking people. now im bored with that too, but i use it to check up on what people are doing and to play the odd 'Which Transformer are you' game, I wouldnt be too fussed it facebook disapeared.
I like Myspace, mostly because of the customisation of the pages and the music, but again i dont really keep up to date with it.
Anyone remember FaceParty and/or are still using it???