Been using launchbox for a while now and I really enjoy the software, but I had to make an account to post here with regards to your contest. I know you're not some big company with megabucks to spend, so a contest seems like a great and cheap way to get some "free" design work done, but you're seriously devaluing both designers out there and your own product.
Expecting people to put in time and effort for free, or at best, for "potential" compensation, means you're going to get hobbyists (or horribly naive younger designers) and an overall lower quality of submissions.
I apologize if this comes across as nagging, but I realize that most people out there don't realize how these contests tend to harm new professional designers from getting work contracts and folks like yourself receiving a better quality of design.
If you care to, this website can explain everything in better detail and with more eloquence than I can, so feel free to give it a gander. It's geared towards bigger companies to some degree, but the overall message applies here as well.
http://www.nospec.com/
With that said, I hope to see launchbox continue to evolve and improve. Whatever decision you make regarding this contest, I hope it pans out for you as well!