I feel like Facebook has become the boring Uncle of our digital lives. Nobody really likes it, except for those blissfully ignorant people who haven't realised how dumb they look posting all the time, but we can't get rid of it. I agree that texting is usually faster than Facebook messaging (though because I use WP7 the line is pretty well blurred between the two for me) but you tend to be Facebook friends with more people than you have phone numbers for and/or text regularly. Maybe this is a little different for you because you are still in school, but as a young adult Facebook is the quick, reliable place where everyone I know is stored.
I read a description of the computer desktop as the place which you can always find on your computer, and so the place where unconfident computer users end up storing all of their files. I think Facebook is the equivalent of the desktop for social contacts on the web. Which I think will give it a lot of resilience to unpopularity, so even if no one loves it, it'll probably stick around.
I use Facebook as the "universal directory" if I don't have contact details for someone, which is the infuriating part. If I need to contact someone I don't have a phone number or some IM contact for, I go to Facebook and look there.
A great analogy would be phone books. I've not found a person who actually likes getting or using them, but they were the best place to find someone's phone number if all you had was a name and a bit of an address.