As a complement to this question about keeping the Mac cool so the fans don't get triggered:
At what temperature does the mac turn on the fans? I know that a high CPU load can cause the fans to go on, so it's not just temperature-based. Are there specific processor temperatures that trigger the fans to spin up?
(I've got iStat installed, so I can monitor the internal sensors for high temperatures. I now need to know what temperatures to avoid.)
My Mac is a Macbook Pro 13" 2.3 GHz Intel Core i5.