I’m sure some of you have already discovered this site, but I want to share it anyway for those who have not. The site is MoiKrewni. Aside from entering your own family tree (optional), you enter in a surname and it produces a map depicting the population with that same surname throughout the country. The information is color-coded by density in different areas. Additionally, you can search by the first letter of the surname. The site is in Polish, but with a Polish/English dictionary, translation site or handy list of terminology you will be able to navigate it.
Another fun feature is the WordPress plugin. If you have a Wordpress blog, you can download the plugin with your surname info and display it on your page!