By default the therm_adt746x module lowers the maximum temparatures. Butyou can control this with the module parameter "limit_adjust".That said I'm not sure if it's wise to increase the maximum temparatures, because it could damage your hardware on the long run. The fan on my pb 15" (pb5,8 1,67GHz) does not run (or very low speed) most of the time. I'm not sure why yours should run significantly hotter.
This is correct but unfortunately the standard values seem to suit the last (1.3 Ghz and above) PowerBook models as far as I experienced.
This means the fan kicks in relatively late if you use the standard settings (limit_adjust=0) and the PowerBook gets pretty hot (at least the 12" models).
You can lower the temperature where the module starts the fan by using the "limit_adjust" value (setting it to -5 for example) but this causes another big problem. The therm_adt746x module shuts down the Powerbook intantly if the temperature reaches a maximum value for some time (not sure how long but some 10 seconds at least is my guess). The default shutdown temperature is 70 degrees C at the processor thermal sensor which will be reached in very processing intense tasks (compiling a kernel will shut down the PowerBook hard - not a good thing)
The upper temperature limit is also effectet by the limit_adjust value and setting it to -5 will lead to a heat related shutdown at only 65 degrees C. This temperature can be reached easily in more or less normal working conditions and renders the limit_adjust option pretty unusable.
Just as a clarification - my experiences are limited to 12" PowerBook models and maybe bigger models will deal with the heat in a better way. But one observation I made is that the hardware, without the therm_adt746x module) can manage its fans by itself - seemingly very much similar to the OS X thermal management. So unloading the module and letting the hardware taking care of itself might be a good idea and should be possible on all of the latest PowerBook generations as well.
If anyone would like to improve the therm_adt746x model I would also not complain. I looked into the source already but my very limited programin abilities (no C at all yet) mean that it will be some time before I dare to change the Kernel myself.
good luck Andreas