QUOTE (suryad @ Apr 23 2008, 08:17 AM)

There are virtually no games that can utilize a quad core.
I really wish people would stop saying that.
Let me put it in plain terms. If an application--whether it be a game, image editor, Excel (yes, 2007 is multithreaded for functions) or any other application--is multithreaded it will use any and all available CPU/cores. The CPU determines which core(s) those threads will run on. Can an application developer artificially limit it to a certain number of threads (i.e. 2 threads)? Yes, but it's generally not recommended to do that, and there's no guarantee that those threads will run on Core 0 and Core 1. Plus, it's not about whether or not the single application is multithreaded or not. If you run multiple applications at once (and who doesn't?) then the additional cores will definitely help.
The price of quad core CPUs has dropped so much that it's almost a no brainer if you're building a new system. Upgrading from a dual core to a quad core is a different story though, unless you're looking for the latest architecture as well (65nm Core 2 > 45nm Core 2+SSE4, Athlon 64 > Phenom, etc).
I'm actually going through this same process right now. I'm about to upgrade my file server/domain controller/one-stop-serving-in-a-box machine and I'm looking at the Core 2 Quad Q9300. I keep flipping back and forth on whether or not to put the Q9300 in my machine and move my X6800 to the server. MHz wise the Q9300 is slower, but it's double the cores, half again as much cache and includes the newer SSE4 instructions. BUT, I plan on running Hyper-V on the server machine with severals VM's running at once so the extra cores would really help out there. Now you can see why I'm conflicted...