One of the new and often unknown features of the Intel Core i7 along with Hyper threading (which gives 4 Virtual Cores extra to the 4 that are already there) is Turbo Boost. It is activated when the Operating System (OS) requests the highest CPU Performance state (P0).

Any of the following can set the upper limit of Turbo Boost:

• Number of Active Cores
• Estimated current consumption
• Estimated power consumption
• Processor temperature

When the CPU is below these limits and the program requires extra power, the CPU will increase by 133 Mhz on short and regular intervals.

To put this into layman terms, if you run a program that is not fully Multi-core aware, the CPU will automatically overclock some of the cores to give the program a boost in speed. On my 2.67GHz CPU, I have seen it rise as high as 2.92 for a short time.  

You can Download a Widget (Vista / Windows 7) to monitor what the CPU is doing at a given time and to see when Turbo Boost is been applied. Thanks to Ken for showing me this link.