There has been this debate for a year or so on different forums on the web whether a person should buy a Core 2 duo processor or Quad. 

The Core 2 duo's (Wolfdale or 45nm) can overclock to 4ghz and use 10% less power. So with most applications you're going to see a performance boost because of the FSB and the higher stock clock of 3.0ghz. $169 for the 3.0ghz wolfdale. 

The Quad core's are a pricey option but you can buy one for $189 right now with the FSB at 1066. Now some people will say that a quad core isn't necessary, but think about this..

If you multitask a lot and play games, keep programs open and minimize a lot etc. The Core 2 isn't going to handle those functions as well as the quad could.

Video rendering is definetely better on 4 cores.

The threading debate is also there but I'll stay away from that.

For people who use computers for the internet and writing papers etc the core 2 duo's are plenty for that, but if you game and do a lot of CPU intensive things I recommend the quad core with go stepping as they call it.

Go stepping allows you to clock higher thanks to improvements to the architecture.