I wasn't impressed. If you have to go to someone's website to view someone's banner, I think it's a waste of time and money. If this banner was posted on like Yahoo or something all the time, then I see some reason to have it.
If you want a great idea, have sponsors pay for your forums by having each member have a signature with a product placement of the sponsor's choice. Course it'll be small, but nevertheless it will be there. How's that sound? How ya like me nooooow?