If you can find a righteous deal on a 6800GT be it used new or refurb then I vote go for it but if you're wanting to upgrade and all you can find are cards at about the same price levels ($380 or so) then you'd be a fool not to wait a month and save a hundred bucks or so. $50 at the very least. I know the prices on the current gen stuff will do exactly like the FX's did, hold tight for about 2 weeks then start dropping like stones once the availability was able to overcome the demand for the 6800's.
The same thing's going to happen again, the 7xxx's will sell like crazy, be higher than hell and be in short supply for 2-3 weeks, after that the hysteria will die down, the prices will drop and when they start approaching the cost of the 6800U's and Gt's those cards will plummet in price just like the 9800's, 5950's and more recently the X800Pros did.
It might take a month or so but it'll happen and not only that the 6xxx series cards will become plentiful in the side markets such as forums and auctions.