Nah not 4, 2 at most at default.
interesting thread. By using the tweak mentioned in the thread performance increases by about 10fps (I've tried this myself) but it doesn't all of a sudden make it more multi-threaded- just better use of the resources. Blizzard have said they have no intention of making WoW properly multi-threaded (even though it absolutely needs it).
That was changed in the last major patch (3.2, I believe). The Default is now all physical cores. If you go in and check the config.wtf file, the modifier is no longer there. If you want, though, you can put it back by making the appropriate entry. I thought about doing that when I built my new rig in late Feb. Then reconsidered and decided to leave it as standard "for a while", and play with it if I saw a need to. So far? No need.
For sure, it loads up the 4 physical cores on my i7. Not fully, for sure, but it definitely uses them. My understanding is that "certain processors"
(rumored to be i7) didn't like the default of 2 cores.
There were a couple threads about this in the Support forum. I'm at work, though, and the official boards are blocked or I'd get you a link.