I am going to be building a new system soon and started pricing various barebones configs + looking at the CPU Charts here at Tom's.
What I find is unless you are looking to buy at least a core 2 duo E6600, then you have to consider the AM2 X2 4600/4800 as well. The E6400 wins no more than 4 or 5 bechmarks vs those 2 AM2 chips and none by more than 10 to 15%. Also, everytime I put together a system whether through an online configurator or from parts, the AM2 system comes out $100 to $175 cheaper. The reason is the motherboards and CPU price. One can get comparable quality Mb's a little cheaper for AM2 - I'm talking feature sets (additional SATA ports, 1394 ports etc.) not equivalent brand for each platform.
So the bottom line, unless you don't think that AMD is going to come through on their promise of socket AM2 compatibility for the K8L and 4X4 AND you are prepared to spend the premium (on price) for a E6600 or higher - the AM2 platform is not to be overlooked.
I'm still at least 4 to 6 weeks from being ready to buy but at todays prices and performance, the AM2 X2 4600/4800 are just as viable as the E6300/E6400.
Because Intel doesn't take the performance crown outright unless you have an extra $100 or so to spend on the E6600 or even more on the E6700.