Awesome - I've been wondering why a service like this doesn't exist for a while. I recon their a quite a lot of people who don't have the technical skills to built their own stuff but need something less finished that a full commercial product - this could be a great outlet for something like that.
Cool idea! One thing you should do is add some feedback when someone tries to reserve a username that is already taken. It currently just refreshes the page. I wasn't sure if it worked for me until I tried something different.
This is seriously awesome. I don't have a 3D printer or any real facilities for making electronics, but I can't wait to see what kinds of things people make. :)