I'm a fan of David Letterman, and not Sarah Palin. Jokes about public figures are totally acceptable. To say that Letterman's joke was outside the normal lines of thinking about mainstream America is ridiculous.
Mrs. Palin, you seem to forget that a good number of your own political party would have one word to describe your daughter when she was pregnant, under 18 years of age and not married: whore. That you did not crucify her is great, and I don't believe she is a whore. You need to look at your political party, though.
And don't take the jokes so seriously. After all, you should be grateful Letterman is not calling attention to your pitiful service record.