This is a slightly premature post, as I'm investigating other avenues at the moment, but....
I upgraded the user registration and paypal add-ons to the latest version this evening on my client's site. When I tried a quick registration via the usual registration page, instead of passing me to paypal to collect payment I was sent straight to the registration confirmation page. When I checked in the dashboard, my user had been created BUT the custom post type that should be also generated hadn't been. This process has been working ok previously. I'm just confirming with the client that she hasn't changed anything else that could have affected this. One change was made very recently to the form to increase the product price, and I'm not convinced they have had any new members since this was done - so this might also have caused the problem.
Can you think of anything that needs to be done post-add-on upgrade?
Is there a way for me to install the previous add-on versions again just to discount this as a possiblity?