I've made a driver for the SUNW,envctrl environmental monitoring subsystem.
It reads CPU temperature, power supply temperature, failure indicators and
also adjusts the fan speed based on how hot the machine is.

If you have the hardware, please give it as spin. It's only been tested 
on the E450;
I'm not sure what other models have envctrl or wether the implementation 
differs.

Files are at http://www.netilium.org/~tnn/netbsd-envctrl/

$ dmesg  | grep env$ dmesg  | grep env
envctrl0 at ebus0 addr 600000-600003 ipl 2024 ipl 2021
envctrl0: Sun Enterprise environmental monitoring
envctrl0: power supply 0: 550W, online
envctrl0: power supply 1: 550W, online
envctrl0: power supply 2: absent
envctrl0: keyswitch is unlocked

$ envstat -r
          CPU0:     49.000 degC
          CPU1:     48.000 degC
          CPU2:     45.000 degC
          CPU3:     45.667 degC
           PS0:     30.667 degC
           PS1:     31.500 degC
       ambient:     25.500 degC
cpufan voltage:      6.286 V
 psfan voltage:      5.905 V
     ps failed:          0
   fans failed:          0

Have fun,
-T