As I logged on to SO today, I was met by the message
You've earned "Nice Answer" and 1 other badge. See your profile.
"Nice!" I thought and started looking around. However, I don't keep track of each an every one of my badges, so finding out which one the other one is, is literally impossible. I know Jeff wants this to be like a scavenger hunt, but I don't see the point in awarding systems of different kinds if you don't even get to know what behavior you were awarded for.
This is somewhat related to this question, but that's about finding out which post awarded you a badge - in my case I just (at least to start with) am happy with knowing which badge.