We have created a very simple customer registration where one can just enter his or her email address and then the system would set this as the new username, add a generic password, which only had to be changed by the user when login next time to add more info into the name/address/etc fields.
Registrations are annoying. People hate them. No matter how clear benefits of registration are and no matter how much of them WILL register eventually, they still hate it. But, in the other hand, they want to finish their jobs online, and most of them are willing to provide some information in order to finish their jobs. So why don't make their lives easier?