My college actually maintained its own service, but it wasn't super-clever and sort of backwards compared to a webapp. You would submit an email to them and they would include your post in a weekly email that went out to everyone on campus.
Good idea ... buy/sell, housing, and rideshare especially
Do you think it would work best if it was walled off? For example, if an @myschool.edu address was required to sign-up/access (similar to what yammer does).
Craigslist works well for colleges with small towns. Thus the load on the classifieds stays low enough to keep track of. Bored students can then just surf the for sale section. In bigger cities it stops working so well, but really, college students mostly have crap, so I wouldn't buy from them anyway. I like to buy from yuppies who are getting rid of their sorta-used couch to get a new better one. They practically give it away.
Craigslist is alright, but it would be nice if you could share things more easily, say with people you know from college/uni. Which is why Facebook should be a good place for ads, but 99% of people I've seen use it just for fun. Those are the problems I have with each of those.
