Yes, I've noticed this even when running with a full team of Tanks, all of which have Taunted at some point.
We've also noticed mobs that are completely immune to Taunt/aggro auras, that literally stand around when hit with Taunt, or standing in the aggro aura. They do not respond until actually struck. Some may fire a ranged attack once the Tank is within about 10', but once they are exhibiting this "immunity" it usually takes a melee strike to get them aggro'd.
From what I recall we actually noticed this prior to the patch, but it seems to be more extreme now (both in number of mobs responding this way and the frequency of occurrence).
'