Why do we pick our nose?

Most of us do it, but few of us will admit to it. If we get caught red-handed, we experience shame and regret. And we tend to frown upon others when they do it in public. I'm talking, of course, about reaching up into your nostrils with a finger in an effort to scrape out snot. Is nose-picking really all that bad? How prevalent or bad is it, really? And why (really, why?) would anybody ever decide to see what snot tastes like?