As the Poles will bitterly tell you, Poland's historical borders are not its present ones. Almost half of historical Poland now belongs to Belarus and Ukraine. Lwów, an ancient Polish city, is now known as L'viv, and firmly in the hands of Ukraine. Wilno is now the capital of Lithuania. It's true that Poland gained a great deal of German land, like Gdansk (Danzig), Szczenin (Stettin) and Wroclaw (Breslau), but, to many, the historical land of the Poles now lies within foreign borders.
It's a shame, for me, really. Traveling to Belarus is kind of a pain in the ass. I do desire to go to these places (Wilno should be no problem though) but seem to be blocked by the need for visas.
I've asked a number of Poles whether or not they'll get back places like Lwow and Wilno, but almost all seem resigned that they'll no longer be in Polish hands. Mostly becuase they think that Germany would want back Stettin and Breslau, which I don't think Poland would be too keen to give up.