I don't think I'll overclock my Q9450 until they are significantly cheaper to replace. The GTX260 graphics card came pre overclocked by XFX which goes some small way to closing the gap between it and the 280 which was stupidly expensive in comparison.
That said, at 2.66GHz, I have yet to stress the system. It handles Crysis with all settings "Very high" amicably. Under linux, the CUDA n-body simulation pushes 18 billion interactions per second.
Pretty nippy.