muse151 - I really hope that since your last post you feel better... but I had to chime in because I have a similar birthmark (starting on the toes of my right foot, continuing bottom of my right foot, all the way up the back of my calf, up the back of my thigh, and over my butt).
Believe me when I tell you that most people don't even really see your birthmark first. They see you.
I'm 33. I started dating when I was sixteen or so. I called my PWS my "jerk detector." If any guy thought I was unattractive on account of my birthmark - jerk alert! Fortunately, I had the pleasure of dating many very nice men... most of whom didn't even realize I had a birthmark and, once they did, truly did not care. One of my very favorite boyfriends (from college, many moons ago, LOL) once told me that when I was born, it was as though G_d had just gotten a brand new purple magic marker and couldn't wait to test it by decorating the most beautiful little baby he could find. I thought that was really sweet.
Next year I am marrying a wonderful man who loves ALL of me, birthmark too.
They're out there, honey. Go find them.