I have the same problem
My iMac worked perfectly before SMC firmware update (iMac firmare is already installed)
In my case, all PowerPC programs that worked fine through Rosetta now frezzes completely the iMac and I have to restart pressing the power button.
Anybody knows how to reinstall previous version of SMC Firmware???
I had not problem with fans, etc. I installed this update because is recommended in Apple Software Update service.
In my case if I run Symantec Norton Antivirus LiveUpdate option, or some options of Roxio Toast 7 Platinum (always worked fine before update) or I try to mount DVD/CD ISO images, the Mac freezes completely
It could be interesting to know how to test if Rosetta is running. It appears that this part of MacOS on Intel is deactivated.
Thanks in advance
Jose