The frontal armour of the King Tiger is reported to have withstood every single round ever fired upon it, a particularly impressive feat of German engineering.
Heavy Armour still has weaknesses in flank and rear facing armour, making it vulnerable to ambush. King Tigers were effective in fighting other armour on the Eastern Front, devastating other armoured brutes.
Infantry with bazookas on the Western Front made short work of the giant, a true David vs. Goliath example.
The bottom line in heavy armour, is only use it when fighting other spires of technological power.
If fighting insurgencies of men on foot, air power is most effective. Heavy Armour is simply a big target to infantry, not only during WW2 but especially today with Asymmetrical Warfare.
Today, most Armour is of the Medium variety, with Heavy Panzers mostly being of the Artillery variety, as they are not required for blitzkrieg assaults. Medium tanks are effective in speed and firepower.
As a defence scientist I continue to analyze and develop tactics capable of leveraging technology against opposition, and encourage the public to fight all forms of government within your nation. Coup d'etat!
There was an evolution of further Heavy Armour in Soviet States as well as the NATO counterparts, until the mid 70's when Armour took a backseat to ballistics and air power.
Tanks still play an important role in warfare today but their use is truly for massive warfare, and not the limited engagements our planet is hosting at this time of writing.
Iraq and Afghanistan are both poor fields of conflict for Armour deployment, Insurgents can easily ambush and assault stationary armour.