Am giving supporter a test drive again and running into the same old bogie-men. I won't flog the multiple-level horse, as it's good and flogged already.
However, here's an interesting permutation:
User signs up for account, opts for "no blog." Just wants luxuriate in the membership happiness of being able to have groups and forums within BuddyPress. Except clicking on the "This feature is limited to supporters only. Click here to find out how to become a supporter." link when trying to create a group yields the skeleton of a blog dashboard (which this hypothetical user, remember, doesn't have) and the message "Nice Try."
Seems that if a user doesn't have a blog, there ought to be a way to have them be a supporter just to enjoy the BuddyPress features.