Well, PM uses popups. I don't mind them as long as it's a popup I instigated (except on my Amiga which is using unregistered iBrowse :-) )
I guess being able to view the whole thread on the reply page (in reverse order?) would be a good compromise. Or, if it's not too much work, how about having three options, selectable in the user's profile settings:
1. Standard (as replies work now)
2. View whole thread on reply page
3. Reply in new window
--
moto