This question has been asked many times, but ussualy it's 148 vs 3700... Actually, I would reccomend the 3700+. The new steppings are supposed to be amazing, people are getting 2.7 and 2.8 easy on air. Opterons have been jacked up in price, and seem to be more hit-and-miss than the new 3700 Sandys.
20110813 - RIP
Take me out into the black, tell them I ain't coming back.
Burn the land and boil the sea, you can't take the sky from me.