Well to answer your question, at the beginning, you pretty much had free reign to make as many accounts as you wanted for the ten dollar's off. However, google cracked down hardcore, and you'll be lucky to get 2-3 in before they start sending you the email of doom and if you go past that, your main google account will probably be viciously closed.
I dunno how they figure it out, but most people say they had the best luck using different credit cards.