The University of Illinois has a neat little thing going on called MakerLab. They have a dozen Makerbot Replicator 2s lined up and you can come in and browse Thingiverse or come in with an STL of your own design and choose from a wide array of colors and a few experimental materials and they help you set it up on the printer. You can hang out while it prints or if you're doing bigger things you can just come back the next day to pick it up. They charge 10 cents per gram for students, 20 cents per gram for members of the public, and double that if you just want to email them the file and come pick it up later (so that they have to slice it and set the printer up themselves). It's a cool environment and I like hanging out and seeing what other people are printing.

I don't know if they're profitable...I feel like all the money they spent on those nice Makerbots will take a long time to pay off. But, they've got a campus full of architecture and engineering students printing off prototypes everyday, so if I was to open a 3D printing store of my own I'd definitely want to be located smack dab in the center of a campus town.