Very, very cool. The fact I'm instantly down my CC info and $60 on three purchases is some incredibly convincing concept validation for myself, but the potential here, both in terms of impact and unique experiences, is unimaginably cool.
One important thing to note, you need to make your referral codes and messaging (i.e. refer a friend and you both win) more prominent. I told my friend about the site and when he asked me for a referral code, I had no clue what he was talking about, since apparently you don't get a referral code if you sign up in the purchase flow and I had to sign up with a secondary fake account to see what the deal was. So you probably want to:
1) Make the referral code actually accessible on the account page (It currently isn't there at all? Unless I'm in some n-way test?)
2) Make the referral code available on every completed transaction. Personally, I'd also recommend tossing in that cute turtle that appears during signup :)
3) Send the referral code, and whole welcome email, for that matter, to the user if they come in through the payment flow.
4) Add an entry on how to find your personal referral code in the FAQ.
Given the empirical success of such tactics (PayPal especially comes to mind) and especially given that many people will want to enjoy these experiences with their friends, you really want to make sure the user is aware of the promotion. Obviously, there are some considerations regarding the cost as you give out $10 and make less than 12% back after fees, but if you're going to run it on the traditional sign-up flow, you might as well put it everywhere. Especially since people who sign up via the purchase flow or make a purchase would be much more likely to refer their friends, since they've already validated the service.
Anyways, congratulations on the launch. See you guys at lunch ;)