Very true. I had a Toshiba laptop that was simply on for the better part of its 8-10 year lifespan, with the result that it overheated a few times due to clogged fans and it was never the same since. Even after I thoroughly blew out the vents, the thermal paste probably spread a bit, and the ambient temperature was always still way above what it should be.

I finally let it die over Christmas. Or rather, I planned to power it up one last time, get fully updated on Windows 7, and then power it down forever and yank the HDD out to put in an enclosure. Of course, it chose to die in the middle of updates. Feh.