Interesting, thanks. But it is still complex: it surely also depends on what you sell and the average customer you have, and also if the users expect to have some advantages by registering.

For example, I personally like to be able to follow the order etc. but often online stores insist that I have to register for anything like this. If the order number and my name were enough, which technically should be, I wouldn't. But having no alternative, I do. So I count myself in "I would prefer not" but you see me registered and count "one of 3 who like registering."