Quad core is a waste of money for gamers, so far there is only one game that uses all 4cores on a quad core, that is Alan Wake a vista only game. But it will work just fine on a dual core, but isnt compatible with single cores (unless using a p4 w/ hyperthreading with minimal gameplay experience)
Maybe within 2 years games will come out that utilize 4 cores entirely but why purchase one now? By the time games finally take advantage of a quad core there will be some really nice quad cores on the market that will put todays quad cores to shame. Not to mention ddr3 will be out by then for mobo's along with the pcie bandwidth increase.
Although there havn't been that many details released about Battlefield: Bad Company, considering the fact that 90% of each of the levels will be fully destructable, I'm guessing this game may take advantage of quad core, just an early prediction.