Poland for instance was basically the largest part of Prussia and from what I've read the ethnic Germans are all but gone from Poland. Also the Baltic states of Estonia, Latvia, and Lithuania, are completely separated and I believe ethnic Germans are all but gone from there as well.
I'm sure it was no coincidence that Poland was Hitler's first invasion (not counting the annexations of Austria or Czechoslovakia) because it had been such a large geographic part of Prussia and he wanted to unite all Germanic peoples and all previous Germanic territory into his Reich. I'm sure he considered all of Prussia proper as a German entitlement.
The part that fascinates me is how a country as powerful as Prussia was basically goes away overnight, "overnight" being a figure of speech, but geopolitically it was gone overnight.