I have been driving around Poland for a number of years now and I have never had any issues with my American license.
Unlike some others I could mention:
Ive been pulled by the Police in Poland twice and never had a problem.
Now the Germans and Austrians on the other hand are fcuking bastards, theyve had 180 Euros out of me over the past 4 months.
I have never been stopped so they do not yet know that I have no EU lic.
Of course, if they ever stop me, I will pretend to be an ignorant tourist (which is easy for me since I am an American) and I am sure they will let me go.