I prefer Twitter, I used to not 'get' it, but during the London riots last year I noticed that the reports of those on Twitter let me know what was going on and where the mobs were a good hour before any official news source.
Since then, I have communicated with experts on eighteenth century history and literature, discovered new bands and generally been better connected to the things I enjoy. It's not a great social tool, but it's a brilliant information one.
Of course the experience of it is defined by who you follow, I mainly follow historians and literature types, and a few jokers.
As for facebook, I forgot my password and can't get a new one sent to my email (because it's an old email) and I haven't missed it at all. Not hearing about Revd Lou's nail polish and Gareth Jones' lunch is not a huge loss.