Non-native scale up is poor, about 40-60% compared to dual, clock for clock. Same goes for double dual core AMD solutions. Intel don't have the same bandwidth to play with, so their double quad cores are going to be 40-60% better than quad, clock for clock or even less.
Unless all you do is encode media files, or run multiple CPU intensive programs, like GIMPS (but not folding at home, because you're better just getting a GPU to do that), it's all just over priced non-sense. Second generation quad and oct core systems are going to be awesome, when AMD bring out barcelona and later when Intel bring out Nehalem and software is built from the ground up to take advantage of multi-core (playing around on a dual core is fun even without optiumization, but I highly doubt benefits from increasing cores to 4 and even worse to 8, without actually running 4 - 8 heavy programs at once).
But oh wells, always the case with 1st generation hardware, 90% of the time its out performed by the currently exisiting matured hardware.
