Philip Trauring has written an article that I suspect will interest anyone with Polish ancestry. He writes:
Many Jewish researchers will find that some members of their family originated in what is now, or once was, Poland. This post is targeted at Jewish researchers, but anyone who has roots in Poland may find (at least parts of) this information useful.
Poland's borders have changed a lot over the years, and what was once Poland might now be in Lithuania, Ukraine or Belarus. In addition, what was once part of Russia, Prussia (part of what became Germany) and Austria may now be in Poland. It's possible that someone lives in many countries without actually ever moving.
You can find Philip's article, Finding and getting copies of Jewish records in Poland, at http://www.bloodandfrogs.com/2011/02/finding-and-getting-copies-of-jewish.html