I live in an area with a high Polish population, so I've met and spoken to quite a few women named Katarzyna. A few went by Kasia, and I think there were one or two Kates or Kats in there, as well. If I were Polish, this is definitely a name I would consider for a daughter, because it's pretty but not too soft (though I'm not as fond of Kasia).
This is a pretty name... but I imagine it would be butchered by pronunciation. Maybe I am wrong though. A real gorgeous name. I just really love it and adore it.