Probably a bit too much. I work from home, using my computer, so keeping Twitter open in one tab has become a habit.
I've been trying to break that habit, though, and am taking regular breaks from social media. Twitter is awesome for keeping in touch with people and finding out what they're up to (I follow a lot of other comic artists+a lot of friends that live far away) - but it can also be pretty stressful and tiring. It's also kind of a time-sink, which cuts into my drawing-time.
But I'm managing it well enough, I think!
On the bright side, I don't have an FB-account, so my social media time-sinks are only Twitter and Tumblr.