Good luck, hope it takes off there! I go to Michigan and this space has become annoyingly saturated...there are 3 or 4 student-startups focused on building a 'Craigslist for Michigan students' and none of them have had an edge. My only advice would be to make your loyal users a priority and hopefully more will come...I'm willing to bet there will be at least one more service like yours that already exists at Penn or will exist shortly.
It's interesting but it feels like every year for what feels like more than a decade, some student is building either a craigslist for campus, a campus chat board, a campus event system, a note sharing app, or course scheduler, or some student discount system. These ideas constantly crop up over and over again yet I don't remember any persisting or growing to dominate the space.
There is such big market for this because college students are constantly looking for cheap things / trying to sell their stuff. I am surprised no one has tackled that need yet. A lot of universities are using Facebook groups for buying and selling, but a lot of stuff get buried that way. I like how simple this interface is!
I wish there were more information on the first page than just the title post, just so you don't always have to click into the post to see things. Price is also a huge factor that is buried!