Most of the time, dual core does nothing for games. Games are very much single threaded. As Ned pointed out, however, with the newest nvidia drivers, and SLI, the second cpu is actually being used, to some advantage. Numbers up to 20% more frames have been reported.
I take that with a grain of salt, as the gfx companies have ways of making things seem like they work better than they do. Still, if you cant notice anything, but faster framerates, it looks good to me.