Fair point. Have you seen http://mailinator.com/ ? It lets you receive email with zero personal details and no sign up.

It would be so cool if Google could engineer that process the other way around. Instead of me giving Google my number, why can I not dial into a phone number of Google (with my own number hidden). I think that would a) get more friction you need against the spammers and b) retain my privacy (at the cost of a phone call).

Thanks, I'll keep that one in mind.