I guess the "like a billion dollars" that Groupon raised last week has pushed LivingSocial to build their registered user base as quickly as possible. And what better way than a 50% discount at Amazon.com, the world's largest online retailer. For $10, you'll get a $20 gift certificate to Amazon.com. It would appear that LivingSocial.com is paying "about $10" for each new user – a high risk play to gain market share in this online local deals space. Whether any of these group buying flash sale sites ultimately gains a strong hold over local commerce remains to be seen, but for the time being, the spoils of the competition are ours. When you sign up through the LivingSocial links on this page, you'll get a $5 credit for a future deal (not valid on today's Amazon.com gift certificate.) And when you share the deal online with three friends who buy it, your deal is free. Hurry, this offer is only good for the day.