I'll echo what some of the other commenters are saying, namely that for anything e-commerce related (and I'd argue SaaS-type software) this method of login make

I'll echo what some of the other commenters are saying, namely that for anything e-commerce related (and I'd argue SaaS-type software) this method of login makes most sense. If you were going to sign up for a free trial of something or create an account at a store, would you want to login with Facebook or Twitter? Or Amazon, whom you likely already trust with your money. The latter I'd say. On the other hand, if I have a social or news/content site, FB and Twitter login makes the most sense. That way I have access to their social graph as well as an indentity. Anyway, this is pretty cool. I think I'll integrate Login with Amazon with my startup (mariposta.com) pretty soon, as it very well could lessen signup friction. We'll see.