When is the best time to make a user create an account?

In the e-commerce arena -- there were actually studies done to examine drop out rates for users creating a profile... wish I could find the studies again to source here, but I will tell you the conclusion. (Keep in mind that brand name of the ecommerce does make a difference in the study. Amazon is more trusted than "Adam's swap shop"). When users were asked to fill out a profile before check out, more users drop out off the site. However, when users went through the check out process and had to submit email/address/shipping/billing information they went ahead a did so. They had to do so to get their order. Creating a profile needs/uses the same information. So on confirmation of order, if a check box is create that says something like "Please save my information for next time" -- you effectively are creating a user profile. Users were much more willing at this point to save their information at this point. In my opinion -- and in my designs -- I always recommend letting the user to perform some actions before creating an account ( if possible). For instance, save something as a favorite (easily session based), then have them create an account when the click on the favorites page.

I always favor website that let me play around for a while before I have to actually register. Think about slick e-commerce websites that let you check things, compare them, evaluate, read reviews and even add to a virtual cart. Then, when you're ready to purchase you can either login or register if you don't have an account. I understand that from some "web2.0" applications the user need to be identified from the start but if your brand is not as powerful as Facebook's letting the user play with a limited version of the website as an anonymous it's still more feasible that asking him "give me your data right away, you'll play later". My 2 cents.