Bah, I've looked around, and can't find a classing thread. I remember that globalsigalliance had one before they tanked.
The basic idea is: Users submit a portfolio of their best work to a special section on the forum.
A panel of mods reviews the portfolio, and ranks the user in one of the following classes: Beginner, Moderate, intermediate, semi-pro, and pro.
It worked really well at GSA, and I'd love to see it here to. Also helps show what you really think the skill in a sig is, by saying "This sig is a high moderate IMO, becasue...."