is not an easy task if there were no tools around to help us, but there is an answer: JetBrains' dotTrace 2.0. It took me only 2-3 ours to download, install, run , and pin point why our CMS site used all the CPU for 4-7 s per request! I did this on a live site - right out of the box.
Instead of guesswork dotTrace gave me an direct asnwer to where the "power leakage" was. And when you know exactly what the problem is - a quick an easy solution is just around the corner :-)
So check it out: www.jetbrains.com