The latest manufacturing revision of 65nm Intel Core 2 Duo chips based on the new "G0" Stepping is hitting stable clock speeds in excess of 4 GHz according to Tomshardware. With the help of some extreme motherboards like the Gigabyte P35T-DQ6 which Gigabyte calls "Ultra Durable 2" technology and some DDR2-1000 high-performance memory, we're seeing dual-core and even quad-core G0 Stepping CPUs reach uncharted waters in Desktop CPU performance.
On the Server side, overclocking is never used but there are significant energy efficiency implications and we'll basically see all the Intel "Clovertown" quad core server chips shift a notch down on the TDP scale. This means the Clovertown 3.0 GHz quad core CPU which had a TDP of 150 watts (used in Apple's high-end 8-core workstation) will now drop down to 120 watts which means it can be used in conventional servers. The 2.66 and 2.33 GHz Clovertown quad core CPUs will drop down to the 80 watt TDP bracket and the 2.0 GHz Clovertown quad core CPU will drop down in to the low-voltage category of 50 watts TDP.
Stepping G0 is probably the last and most mature version of Intel's 65nm manufacturing before Intel switches to their new 45nm High-K dry lithography manufacturing process which will launch towards the end of this year.