Some users email-activate, some don't
 

Has anyone managed to hack anything together to allow some sort of flag in the registration system that determines whether or not a user should have to activate by email or by activated straight away?

What kind of flag you are thinking of? These are people who didn't sign up yet, so they don't have a user record, and nothing you can set.

To do what I needed I guess I would have had to have a second register.php hacked up so as to avoid the email being sent and the usergroup being set to the "waiting for activation" for people who were paying for membership.

It now looks like, as I'd hoped, we are going to make everyone verify their email for the forums so it's no longer needed.

Thanks for the reply though.