The Core2 Chips are simply faster than X2 chips at the moment.
AMD has slashed the prices of their CPUs and Chipsets so that they may make cost analysis sense even though they cannot provide the same level of performance.
AMD is in the process of preparing to ship the Phenom which is their next gen processor. It appears as if this will make the clock for clock performance much closer, though this chips will not clock as high as the Intel chip.
Truthfully, either chip would be a good chip for many people.
For the average person, all of the CPUs give plenty of power.
For the most part, Gaming is what requires the most power for home users.
Gaming relies more on Graphics power than CPU power.
The current big advantage for Intel is its ability to be overclocked by enthusiasts. When looking at retail systems that cannot be OC'd, then Intel stands out less.