Another VM user so another vote for quad core. You can really feel the load of running a virtual machine if you have only 2 cores. If you use Aperture, Final Cut X, or Handbrake (just 3 I know) you will definitely want the quad core.
I have the Quad core 2.2 i7 in my MBP. It's very speedy. I recommend it. As things advance, quad core is becoming more common and more software will be better equipped to leverage it.
There's nothing wrong with dual core, but quad core can just handle certain stuff better, even with the slower processor speed (which is really pretty minimal, at least for 99% of what most people do on their computers). I can process some heavy duty Photoshop stuff pretty quick with mine; in fact, the sill on my machine hardly ever gets more than mildly warm.
Go for the 2.2 i7, and then spend some money on doubling up your RAM.