Part of the issue with the idle droop has to do with the location of the throttle body on the PD supercharger setups. Since it is moved from the stock location to the back of the supercharger, we introduce a lot of throttled volume to the system. With the stock setup the computer can react a lot quicker to load changes at idle since only the intake manifold is the throttled volume. With the intercooled supercharger setup, the intake manifold, charge tubes, intercooler and supercharger all become throttled volume. So when the ECM needs to add air to the system for increase in load, it is heavily buffered by all that extra volume. We have been working for awhile on tweaks in the program to make the ECM respond quicker to this load difference, and have made minor improvements over time with it, but the extra volume in the system really makes it tough. Also different cars are more prone to it than others, some idle like champs and some take the little dip sometimes.
And there you have it

. I had the drop/shudder for a little while with STII without A/C on. It did go away after a little driving. It will still do it now with the A/C on. But as Dave said, because of the location of the TB, the change takes a hair longer to reach the combustion chamber. For me it's not an issue. I can probably count on one, well maybe two hands how many times I've turned on the A/C in 3 years.
scdyne, the mp62 DDM uses has a vacuum controlled bypass valve, so it does not apply any boost at idle.