8 core Mac not really 8 core?

I have a couple of the aforesaid Dell dual-quad-cores (I ditched some Mac Pro quad-cores recently) and for regular stuff, it's slightly depressing how little the cores to get used. I have some stuff which actually does use all 8 cores and that speeds things up by quite a lot - but as several articles have pointed out, the real sticking point is the memory and the subsystems and how they interact with the two processor sockets when those sockets are both running quad-core.