There are going to be the odd few that are going to upgrade solely to build a system around the Conroe that already have very high specification equipment at there disposal, but they have a very high disposable income or are caught up in the hype of this CPU.
For most enthusiast to cross over to Intel at this moment "IF" they already have a very high standard rig, the gains that would be made from what I can gather would be negligible. You have to upgrade several elements of your machine, motherboard, Ram, to house the CPU. Your talking £600 for the E6600 and decent mobo and 2GB DDR2 ram. That is not cheap for what its bringing to the table at this point with regards to gaming.
Waiting for the release of the Dx10 cards arriving in a few months, and saving your hard earned cash for its arrival, will make the whole experience of crossing over that more pleasurable. More toys, more to play with = more fun. Not only that, a lot of the problems will have been ironed out regarding bios updates and compatablility issues. There will be atleast 20 new motherboards on sale, a little better value for money too. The savings you make will go towards your Dx10 cards!!!
Having said that, most of us will still be using dx9 XP, but there will still be huge improvements made in dx9 with these cards.