Dual CPU is not CPU A + CPU B.
To get full advantage of dual operation applications must be compiled with "multi-thread" or "multi-processor" operation.
For example, if you play WarCraft on a DUAL 1.2GHz, the game will run like if it's on single 1.2GHz processor. But, on the other hand, the OS, can use the other 1.2GHz to do other stuff (video compression, etc...).
One of my friend made this mistake 2 year ago, he bought a Dual Duron system! He tought that the speed would add up. But this was not the case. He returned back the rig and bought a single processor system.
Dual CPU is for specific software or condition. And by the way, AMD CPU scales better in Dual mode than Intel CPU.
This is short, but, I wish this will help you!
Would you buy a GPS enabled soap bar?