They use a tick/tock cycle for die shrinks - I usually buy on the tock side of it. Die shrinks usually bring lower power and other incremental improvements that weren't in the original silicon.
I simply see no need to upgrade, my Q6600@3.2GHz in my tower handles everything I throw at it, and the i7@3.33 in my laptop is similarly adept at getting things done.
I think an SSD would be a better speed investment for a lot of people, because I am very rarely processor limited. I likely won't replace my stuff until it totally breaks, which might take a while.
There is a point which computing is turned into a commodity and people can no longer perceive improvements. I doubt a person not doing CPU heavy tasks like video manipulation would tell the difference between a 20GHz CPU and a 30GHz CPU.
At that point we've got one foot in the Singularity and we'll be to busy in our holodecks to care about how "fast" a CPU is on paper. It's going to be an interesting 20 years.