I like Q6600 BECAUSE I don't need it. This way when I do need it, I have it without additional cost. With a dual core now and a quad in a year, the money spent on the dual core is wasted.
$200 DC now + $200 QC in a year (estimated, might be less...) = $400
$260 + nothing = $260
Makes sense to me. Same reason I don't recommend buying XP. Money will be wasted once you buy Vista, might as well get it now. Assuming you need to buy an OS for a new rig of course...