It depends if games can take advantage of multiple cores. The games I'm playing right now X3: Reunion and X3: Terran Conflict (both space sims) unfortunately only uses one core so Dual or Quad doesn't make a difference if both are clocked at the same speed.
On the other hand, encoding video file using the X.264 codec and Handbrake utilizes all four cores in my quad. Unfortunately, encoding with X.264 is rather slow compared to other video codec because it is pretty demanding. Maybe I'll upgrade to an i7 CPU or wait for the next generation CPU.