Intel's Penryn generation of Yorkfeld / Harpertown CPU's are going to continue the good transition of the great overclocking.
The new CPU will even be able to go beyond 4GHz as the current 3GHz QX6850 can do up to 3.6GHz, but the new 45nm one will need less power and won't be that hot.
Whenever Intel launches 45 nanometre Quad cores for desktops you can bet they will go over 4GHz, but not much faster than that. This should be sufficient for most of us and it will hold the water until Nehalem later in 2008.