Sure, your computer works at 3Ghz but what about your brain? 

"The Brain Fitness Program from Posit Science focuses on auditory processing—on improving the speed, accuracy and strength with which our brains receive, record and recall what we hear. This is closely related to our ability to communicate clearly, think quickly and remember fully." 

The test will take approximately 10 minutes. Pretty cool, but make sure you got Windows; it doesn't work on anything else.