Most of my close friends aren't. I wonder why. Twitter seems to be more of a celebrity thing than something ordinary people (like me) would spend time on. I think it's a pretty cool site, but I just don't find myself inclined to post updates there often.
I should probably keep my profile private so I'd only read tweets of my close acquaintances and have my tweets be read only by people I actually know. But as I said before, most of my close friends aren't on Twitter so what's the point?
Twitter just doesn't do it for me (as of the moment). Maybe if I get a tweet from Adam Levine, I'll be more active in it. Haha.