I have an account that I use all the time. I prefer other sites to facebook, but, facebook has critical mass. Also it's not really an either/or, I'm pretty much always on Twitter too. Ah, the joys of being able to have multiple windows open, even if you only glace at them once a day.
I have one, but I don't personally update it regularly -- mostly just use it to keep in touch with old friends via the messaging and chat systems. It's pretty nice for that, since essentially all my friends from high school/college/the Army use it as well. So I picked "use it all the time" since I'm definitely on more often than once a month.
I have one, I frequently want to get rid of it but I like having access to old friends. I seldom post anything on it, at least until just this past week (when I was on a lot of pain medication after surgery) and got this strong urge to post a bunch of political rants.
I've used it for a few of the game apps it has that amuse me. Set it up originally when I was trying to get somewhere with League of Legends due to the bonus character and skin unlock.
I have a Facebook account, and I check it occasionally to see how my friends (those I don't see so often these days) are getting on with their lives. But I don't really do anything with it - it holds no real interest for me (certainly not in comparison with this place here) and I struggle to understand how people can (and do) become so addicted to it, to the point that there are people that seem incapable of going even a couple of hours without doing something on Facebook. Shallow^ seems a rather appropriate word in the context of what most people seem to do vis a vis Facebook.
I have a Facebook page that I log into every day; I use it mostly to keep up with actively-updating pages of things I like, but I also use it to keep up with a few of my extended family members and various IRL and Internet friends. A few years ago I used to play a couple of Facebook games as well, but I've dropped all of them since then. As for other social networking websites, Myspace is dead and was crappy in the first place, and Twitter can go sit and spin as far as I'm concerned.
I don't really tend to read or post status updates, but I check it every couple of days in case someone's messaged me or something.
Use it fairly often. I have a lot of friends who live some distance away and it's a good way to keep in touch, organise events etc. Plus I'm lucky in that if my friends post something then it's normally of interest to me.
I'm slowly losing any attachment to it at all. I may not delete it, but I won't check it more than once a month. Thing is, Facebook will make you more lonely at the worst times. That Friend list....isn't. It's a 'random pricks and aquaintances' list. People collect each other like fucking Pokemon. If your actual friends aren't available, who you'll be in contact with in better ways, and you're feeling down....you've got that number next to your 'Friends' list just making you feel bad about how many people don't give a shit and aren't there for you. It's like the world has found a way to put a hard number on misery.