There seems to be a possible way tho. A program called Active@ Hard Disk Monitor will tell the usage in time that hard disks are active at least on my systems it seems to be fairly accurate. I installed my WD drives new at the same time I built my system (around the middle of Feb) and the time it shows looks to be about correct (since I built it it has been down less than 24hrs total). I also Moved one to a system that isn't always on 24/7 (because of a failed segate 7200.11 drive) and to make sure that it wasn't just counting the time since 1st installed I included a shot of that also. The times list on both seem to be about what I would of expected.
But as far as I know there is no way to actually tell how long a cpu has been run or how it has been run from the cpu itself.
On these shots you can see the times listed in the box on the bottom left corner.