On any given day an SB-800 speedlight will still sell on eBay or elsewhere for over $450.
A brand new SB-900 can now be bought for as little as $550 from overseas so why are the 800's still pulling the money they are?
I've heard a few grumbles about the 900 with regard to overheating and cutting out. Could this be why 800's are still so popular and sought after?