Well, the prices will be determined based on supply and demand.
My guess is that in the short term, 40D's are going to drop in value, especially if the 50D proves to be the superior camera that it is on paper. The 5D should also drop a bit, but how much will be determined on the cost of it's successor.
Lenses are different, and really the only thing that will drop a lens price is a replacement being announced or the addition of a lens as part of a mainstream kit, like the 28-135mm or the 24-105mm.
