Wishbone: For the record, I think contests that require the use of social media are not about "giving back to the community". It's buying advertising, pure and simple, and buying it dirt-cheap to boot. It's getting thousands of people to advertise your product/company, and only having to pay a few of them.
I'm not saying it's not a good idea, it's just something to think about.
I agree (mostly), but In this instance I dont mind advertising Swing Swing Submarine a bit, since I like their game Blocks That Matter. But one thing to keep in mind is if you dont want to freely advertise the company via social networks, you can easily remove you tweet or unlike the post once the contest is over, so you only advertised them for a day or two.