Except that it's where the people that I would choose to socialize are. My twitter social graph is has nearly no overlap with my FB graph. For me twitter is mostly writers/literary types, FB is mostly people I know in real life (although most of my interaction on FB has been with interest-based communities for which no analogue exists outside of FB).

That said, I'm doing a social media fast for Lent. It's entirely possible that when Easter comes I might not go back to either Twitter or Facebook.