I hunted all over the site and could find almost no information about what being a premium member means (not that it needs to mean anything other than you like the site and want to contribute a few shekels). I'm surprised that there isn't more obvious information on being a premium member in FAQ and other forum documentation.
FWIW, I learned that I get to put a few self-chosen words next to my avatar. It's worth 3 times the price of admission.
Thanks for listening.
We now return you to regularly scheduled programming.