i'm going for the 2.66. i figure the extra 2.66GHz (.66 * 4) is worth the $300. Although, I don't consider the extra 1.33GHz you get with the 3GHz to be worth $800... half the speed increase for almost 3 times the cost.
if you're interested in the 2GHz, you're in luck... it's starting to ship. now there's just a wait for the ATI graphics card and 3GHz processor.