I read, and I believe, that you can significantly increase a CPUs lifespan for each 5 or 10 degrees you lower its temperature.
Personally, I am not comfortable with the temperature my Macbook runs at left on its own; I am convinced Macbooks are not adequately cooled/ventilated. I use a specially designed fan behind it and I keep it raised about a half inch from the desk. This usually keeps the temperature around 48 C; unless I am scanning with ClamXav or something, which tends to raise the temperature.
I use Temperature Monitor 4.x.
I see iStat is freeware as well so I will download it and try it.