We have been using such site for a long time in PF, particularly in the thread "The meaning of your Polish last name" (3021 posts so far).
It is based on the same engine as many other sites elsewhere: Germany, Austria, Switzerland, etc. You have to watch one thing: it does not recognize that -SKI and -SKA are the same names, so you have to test it twice to get totat statistics. It is also very sensitive to diacritic signs, so make sure to put them wherever needed.
I believe that data collection in Poland is based on PESEL numbers; in Germany of phone lines.