1. The Facebook isn't going away. While Facebook.com may not last forever, a service like the Facebook will always be present and useful on a college campus. The logic to this is quite simple: students are forced to renegotiate their social networks every semester. The Facebook supports and answers the student's information needs. Put simply, our students are curious; they want to know anything and everything about the students around them. If you had the Facebook when you were an undergrad, wouldn't you have wanted the same?
2. Almost all of your institution's undergraduates are on the Facebook. I found that 94 percent of UNC's Freshman class was on the Facebook. Techcrunch reported in November that 85% of all college students were on the Facebook, and surely that number has increased. You can't fight numbers like this. More importantly, you can't ignore them.
Both of these services can provide useful tools that can be utilized from home, office, or dorm room.