In addition to what Jack said, I use 3DMark06 as a gauge for whether the last change I did in BIOS for overclocking helped or hurt. Nothing like getting the system to boot up and look good, then after starting the test, find out it fails after a minute or so. Running it at the same time as I run Prime95 also gives the system a very good stress test.
A thing I did find out was after a certain point, boosting the cpu speed did very little as far as the 3DMark06 score. Then it becomes a matter of better graphics cards then anything else. Overall, I find its only a test to best compare changes that I make to my computer, rather than my computer against someone else's computer. Well, that's my 2 cents worth.