how is that acheived kevin? would be interested to know 
There's a parameter, accessible by Tech 2 that you can set to calm down the automatic fan control. I'm guessing GM got lots of customer complaints in the early days so added a setting that dealers can use to appease customers who didn't like it.
From what I have noticed, the effects appear to be:
The fan control is much less frenetic. It would previously go to max speed if the temperature deviated by a degree or two from the set point. It now only seems to use high fan speeds if genuinely required to maintain temperature, or where the car is very hot and maximum air con effect is required.
During steady-state driving at a stable temperature the minimum fan setting possible appears to be used. Beforehand, I always felt it used too much fan, causing me to constantly turn it down.
One you have taken it out of auto and set a fan speed manually, it stays at that speed, even if you change a temperature setting, for example. Previously, it would set the fan back to a high speed as soon as you touched anything else.
Depends on your preference. Some people don't have a problem with the standard behaviour, but of all the people for whom I've changed this setting nobody has asked me to put it back again.

Kevin