For most people, there is a lot more than just a degree to seek out in college. I'm no big fan of Facebook whoring myself, but while it obviously doesn't replace stimulating conversation or actual time spent together with good friends, it does provide a lubricant for them. My guess is that when all is said and done, you'll value your social ties and personal development a lot more than your knowledge of red black trees.
P.S. I don't mean to suggest people blowing off their classes to use Facebook is the way to go, but I think that to suggest it can't have value is somewhat silly.
It certainly does have value, but considering how much people pay to go to college it seems wasteful not to take advantage of the classroom resources. Going to college is great for finding a co-founder, making friends, etc. Whether class time is well spent doing those things, however, is less clear.
It all depends on the class and the context of the college.
I Facebook in a few of my classes. Sometimes it's because we're going over something I learned when I was younger. (I know how to use Final Cut, for instance, even if I'm completely clueless about sound/lighting setups on a movie set, so despite one class's being productive there're interludes where I don't need to focus as much.
I have other classes, however, where a good part of the focus seems to be on socializing. My entire major is devoted to entrepreneurialism; a huge part of the major is meeting other people and getting ideas going. So classes often have a relaxed environment in which people are encouraged to talk to one another. Facebook's useful there, also. I personally find it much easier to judge people and their ideas online; in person everybody seems beautiful and brilliant.
A huge part of what you get when you pay for college is access to all those people. Classes are valuable on one level specifically because they put you in a defined context with a slew of other people. I'm a people person, but I hate randomly going up to people, and I don't like talking to people without there being a reason for us to talk. Classes connect me to people, which is just as valuable service as the things I learn.
I'll also add that in the group I'm working with right now to launch things, all the communication's handled entirely over Facebook. We tried Backpack and Skype and Google Wave, and none of them could handle the conversation as well as informally talking to one another on Facebook did.
P.S. I don't mean to suggest people blowing off their classes to use Facebook is the way to go, but I think that to suggest it can't have value is somewhat silly.