From a consumer psychology aspect, having to "sign up" for a possible 1 time purchase can definitely be a sales barrier (in my opinion). I understand the pros of being able to track purchases, etc, but (for this particular site) i think is unnecessary in this case. I would like to know just how difficult it is to remove this function all together. If it is too crazy, then it stays in. I have seen in the forums where others have tried to just disable the password part of the procedure, it that seemed very difficult.
On the flip side, for another site i am building where this is a good function, how difficult is it to ADD a link to a permission based 3rd party email supplier? Their forms are very specifically coded and i think (not sure) it would be difficult to add their form/code to the PowerStore registration page.