There are a hell of a lot of people who use their PC primarily for gaming.
Yup, and they'll also benefit from multi-core CPUs. Most noticably, the game will be able to run on one core, while all the Windows services run on the other. I know there is no 5GHz CPU - that is my point.
Nor is there likely to be one, until we can reliably prevent (or at the very least, predict) electron quantum leaps (not something you generally want to happen inside your CPU). Right now, if you're buying, Intel Core 2 Duo is your best bet.
Personally I'd go with an AMD. Unless you actually want 3 pounds of copper on you CPU in order to keep it cool enough to operate.