Why? You'll gain virtually nothing performance wise, not to mention the fact that a large number of laptops have the processor soldered to the motherboard and therefore are not upgradeable.
I agree with bubblehead. Upgrading to a 2.8 ghz cpu won't really improve anything. Also, upgrade parts in a laptop is pretty much pointless as you can't really upgrade anything on a laptop. If you have a core2 cpu, it's time to buy a new one.