Unless you have your heart set on quad core and perhaps even if you do, you might consider that the Wolfdale/Penryn's are due out like any second now. They aren't a huge increase in performance over what is out there now, but the smaller, newer process and larger cache (6mb vs 4mb) do show a performance increase as they should. And supposedly being 45nm makes them much more overclockable if that's your thing.

It sounds like the E8400 should be right around $200 (usually the prices they show are the prices that a builder would see in very large quantities) and it's 1333MHz FSB with a rated clock speed of 3.0GHz for the sake of comparing it to what is available now. Intel has actually been pretty good lately about replacing an old line with an improved line at about the same pricepoint instead of making you really pay through the nose for new tech.

Even if you still want to go with a Q6600 or any Conroe-based chip, the Penryns might drive the price down a little. It won't be a huge decrease, especially since there won't be quad core versions right away but I would think it's still worth waiting a week or two to see what happens. And no matter what you decide to do, it wouldn't be a bad idea to make sure the board you get will support Penryn at least through a BIOS update. That will almost certainly be your upgrade path even if you don't want one now.

I would personally go with an E8400 over a Q6600 at this point.

- You get a faster chip for quite a bit less money.
- Very little takes much advantage of multiple cores right now, and that doesn't seem likely to change any time soon. While you could argue that you could just load many single-core programs, this will be taxing on other systems like file I/O, memory, and video performance. And I'm not even sure how it would compare to just running the same processes on fewer, faster cores anyway. In that situation you aren't really getting the parallelization which is what makes having many cores especially worthwhile, you are just "making up" for CPUs not being as fast as you'd like for them to be.
- Newer tech. Not only would a 3GHz Wolfdale be faster than a 3GHz Conroe (anywhere from 4-10% it sounds like), but they also include new technology like SSE4. One of the rare cases I would say to automatically throw more cores at an application would be video encoding, but they're saying that SSE4 will be a pretty considerable improvement once software starts taking advantage of it.