That's a great point carol - but the solution i adopted does NOT require any connection between your paypal account info and your forum account info.
I know that people often like to keep such things separate and not use their good email for signing up at forums.
What happens now is that when you make a donation you are sent an "activation code" which you can use to activate any one (and only one) forum profile.
So basically after you donate you get a license key for our programs and an activation code that will let you activate any forum login you wish.
I'm a bit proud of the solution actually
(much of the motivation for automating this was just exactly for the reason you site, that it was a pain for everyone to have to coordinate between donations and logins - now you don't have to worry about it at all).