Hello. My name is Karin (Care-Rehn). While in Germany as a a teenager, I found my name to be common there. I asked how they would pronounce it, and they said it the same way I do. Personally it drives me nuts to be called Cah-rin, but that is due to association. Anyways, that's just my 2 cents. :D I do have a wonderful friend who's name is Carren (Car-Rehn), and I think it's beautiful. It drives her nuts, because nobody get's it right.
I am a Karin (pronounced CAR-in), but I also know a Karin who pronounces it like Karen. Most Karins I've met (which are few and far between where I'm from) pronounce it the way I do.