I use both equally: little to never.
Twitter I have to basically just follow people, which isn't really my thing anyways... If I were famous, I'd use it more, but that's all circumstantial.
Facebook I have basically because real-life people exist, and get annoyed whenever I don't friend them or something. I would not use it, but practically everyone knows that I'm into computers, so they'd just get confused. I know that the only people I care about would ever message me or the like, so if they tell me I missed some event they posted on Facebook, I just tell them that I never use it and they're usually okay with that. Trust me, it's simpler this way.
Email is still my favorite means of communication. :D