An old saying in the world of computers goes something like this: "They don't stay on top for more than 2months, there's always something better the next day"
That's regarding to performance/$, and maximum performance once scaled to maximum obtainable.
Soon C2D will have its fair share in performance/$ and it'll be time to move onto another. And it's a lot sooner than you think.
With technology, there's always something bigger and better on the horizon.