I'm not a gooroo, but my guess:
Given the drop in fuel prices, I would guess that the TDI market will soften through the winter a bit. People are going to be more content with their gassers at the current $2.25/gallon (and we'll see how much more it drops.) Fuel supplies are rumored to be high, so that should keep prices down. I would have to bet that we'll see $3/gal fuel again next summer, though.
There are still no new TDI's available. This will keep supply down, even through the re-introduction of the common rail TDI's for the '08 model year. New ones will be scooped up quick initially, and likely for MSRP. Maybe even 'market adjusted'. But there will still be many people who don't want to buy new, or can't afford to buy new, and the demand for scarce used TDI's will keep prices up for the first year or two into the TDI re-introduction.
Personally, I'm thinking it might not be a bad idea for me to pre-order a new TDI Golf. That way, I can sell my used Golf in a higher-priced market, before VW is able to meet the demand with more product and prices come back down.