multitasking
People forget that OS X is unix, it inherently takes advantage of multicore. Boot up, and before you open any apps, run top or activity monitor just to see how many running processes are out there.
Personally, I have 3-4 terminals, 2-3 virtual machines, and 3-4 apps running all the time. Even if none of them were multi-threaded, they still are unique processes that can be scheduled on any core.
More cores = unix goodness