@Phoenix32890,
I joined a while ago, expected to like it, and didn't. I'd check in, nothing much would've happened, I'd wait longer to check again, there STILL hadn't been much... and then I just kinda stopped looking at it.
It laid dormant for maybe 6 months to a year (I forget) and then it became the main place for activity around my 20-year high school reunion. My friends list exploded and THAT's when it started getting interesting. I only really started liking it after my friends list hit about 40. Like A2K, there are some frequent posters and some who mostly lurk, and to get a critical mass of the voluble types you have to get through several lurkers too.
What I absolutely adore about it is the community aspect (like, local geographical community). To take a random example, one of my friends posted that the police had just come knocking on her door asking for info about a robbery suspect that might've come her way. A bit later, another friend who lives near the first one but who doesn't know the first one posted that she was freaked out about helicopters hovering over her house -- I ventured that it might have something to do with the robbery. A bunch more stuff trickled in, I introduced various people who didn't know each other, we all sat there with bated breath (it was an armed robbery) getting real-time updates from people who saw one thing or another (I was Googling repeatedly but nothing had made the news yet), and then the guy was finally arrested in the very first friend's bushes. (Of course. She's the kind of gal who has a very INTERESTING life and it was extremely fitting.)
There's a specific usefulness to me because I can't "overhear" things IRL -- I've learned SO much from Facebook stuff about my community and the people in it. I've made a few friends basically just through Facebook (we kept seeing each other comment on mutual friends' status updates and then eventually became friends with each other, or we were nodding acquaintances and friended each other on FB but really got to know each other through FB).
In the same category, I've gotten to know a few of my husband's family members better -- family reunions suck for me in terms of lipreading load/ communication, and I tend to revert to nod-and-smile to get through it. One uncle has a really great acerbic sense of humor and I'm much better able to engage with that in a written medium. (I think I shocked him a bit at first, he may have thought I was a bit more meek than I really am.)
A good friend of mine from high school who lives in another state and who I'd barely talked to before re-connecting with him on Facebook during the Great Reunion Friending just bought a 3d printer kit that he's putting together (SO COOL) and sozlet saw it and became obsessed with it, I mentioned that and he gave a link to some free 3d modeling programs and said that he'd go ahead and print something for her if we sent him the file.
Etc., etc., etc.
I, personally, adore Facebook.