One of the best technique I have ever seen as a user/customer is being able to do the entire call to action without having to log in / fill out forms.

eg: if you're going to sell me something, try to convert me into a longer time customer / account holder AFTER you've sold me a product.

It essentially means creating accounts on the fly based only on an email address.

Agreed. Too many startups are focused on connecting to the social graph instead of selling a customer on it. If they like your product, they will make sure their friends are on it or hear about it.