More likely to be eaten by Polish Americans than by Poles. Ate it often when I was growing up in Scranton. You could even buy the blood in the supermarket. But never even saw it during my twelve years in Poland. Can't even say I ever met any Pole who ever ate it, in fact.
Delicious, if homemade. I had it in a restaurant once in Chicago, though, and it was God awful. Nothing at all like the homemade version.