I know there was a hack similar to this previously, but since 6.2 it hasn't been updated, and I'm not one to just blindly try it to see if it works because I don't have the time to tweak it.
But really, user groups are a very major part of my community, so this could be something really used. I don't need group specific graphics or anything, just a simple "Gold Member" under their avatar would be all.
