Fantastic thread here a year ago - but never finished:
Precisely the same problem I have. I am unwilling to send a user away from the shopping cart before they purchase to register - however, I need all purchasers to also be users in Wordpress.
I expected marketpress to create users for the people whom are buying - but it is not. Where/How can I hook in to create a user upon completion of check out? This is a common functionality of a shopping cart to create a new user, is there any plan to have this be a feature?
I assume this is a common issue - has anyone hacked through it that can provide the code they used?