Spotted this great little article over at Neowin.
Unfortunately, even some of the brightest people I know are subjugated to the megahertz myth...that more megahertz means more power. Intel established this as their method of rating processor speeds long ago, and as such, John Q. Public has fallen victim to these beliefs that the processor clock is all that counts due to Intel's obvious dominance in the processor market. How then can an Athlon XP 1800 (1.53GHz) beat a P4 2GHz?
Glad you asked! In reality, there are many factors that contribute to a processors speed. For the sake of simplicity, we will ignore most of these such as architecture differences & development controls (SSE, MMX, 3Dnow!, etc ) and try to stay focused on the speed equation, which as you will see, quickly dissipates the thought of more megahertz alone means a faster processor.
Full article @ DataKill