A while back I installed Windows Vista on a Dell Latitude D810 laptop. Given that Vista's Resource Monitor now provides more information, I noticed that my CPU wasn't running at full speed. What was unfortunate was that this machine was out of warranty and so I had low expectations (which were met...) for Dell Support. Their best suggestion was reinstall XP (which, I'm sure you are not surprised to hear didn't change a thing).
Jump to the present. My other Dell Latitude D810 started running slow after a system board swap. Speedstep tools, cpu-z, and other tools were all reporting that it was being clocked down to about 800mhz.
Jump to the answer. The problem was that the fan above the graphics card was unplugged when the tech replaced the motherboard. After plugging it in, everything worked fine. Running diagnostics on the other machine indicated a similar fan failure.
So given that the operating system was clocking the CPU down because of a fan failure, couldn't there have been a visible system alert that said something? I mean, I can have a tray icon tell me that someone logged in, why can't I have something that says "your fan is broken"? Instead, it all looks like magic stuff is happening in the background....