Ignoring the fact that my phone has had the signal problem since day one and is still unusable without a case (just picking it up with my left hand would kill all signal), amazingly my 4.0.1 iPhone 4 now gets 3 bars where it used to receive 5.
Fine and dandy, but from the same location I have always had full bars both with this iPhone, my last iPhone and a half a dozen other AT&T phones over the years.
This is because you were not seeing an accurate representation of your signal with your iphone prior to today's update.