Updated to 10.6.2 and once again, my iMac sounds like a jet engine again and it's heating up like a good'n. I fixed it in 10.6.0 by reseting SMC and PRAM, no such luck this time - It's back to 10.6.1 for me then. 🙁
That happened to me too. It also happened when I updated to 10.6.1. The restarted dozens of times and reset the SMC/PRAM many times as well. I had to end up reinstalling Snow Leopard and reapplying the updates. If you just put in the disc and boot from it, it should reinstall without erasing all your documents and applications. That fixed it for me.