That's what's used in tzatziki, the cucumber sauce that's served with gyros.
mmm, gyro with tzatziki. . .
Yeah...I am sorry - nothing can replace sour cream in my opinion. I love that stuff. I would rather have a tiny dollop of it than a huge dollop of lowfat sour cream or yogurt. Same thing with mayo. Give me the real thing in small quantities or nothing at all.