I spend more time there than I'd like to admit.
See, here's the thing. My uni classmates (a media course involving a lot of practical film-making and stuff) use facebook to organise stuff, so professionally, I kinda have to check it regularly, more than once a day, sometimes I simply have to keep an eye on it all day if the people I'm working with are particularly disorganised to the point where they'll basically say "Okay, we're shooting now, meet us on the other side of town in ten minutes", and if I don't reply or turn up quickly they just assume "Well, he must be lazy" and start without me.
So, that's quite a bit of time I already HAVE to spend on there.
Then there's social stuff. Again, people use groups, they use messages, they use tagging, so if I want to know what's going on, I go to there. So yet another reason I have to keep checking.
Then there's my youtube. Aside from the odd time I've posted a video here when it's been appropriate to do so, facebook is really my only way to get more reach, even though at the moment it's only really my friends who are subscribing, so at some point, that's gotta change, but at the moment, by best option is to share every video I make on facebook.
So, if you put that all together, there's so little time when it isn't necessary/useful to be on there, that I'm often on there the better part of the day, though I'm not necessarily active all the time, it's often in the background where I can check it easily.
I do enjoy using facebook. Sure, I have a couple of annoying people who post hipster photography and stuff that I keep on my friends list essentially because I have to work with them, but mostly I just chat with friends, find out what's happening when, all that good stuff.
I just wish more people would communicate in at least some other way, I guess.