You're absolutely right - the left, not even the loony left but even just the left and moderate left, are terrified of Mrs. Palin. She is everything they have always claimed to stand for; smart, successful, driven, independent, etc. Everything they've been telling anyone who'll listen is a good thing, what they promote, what they want, yadda yadda. Only one horrifying, terrible problem with Mrs. Palin - she's GOP. Worse, she is an honest-to-God conservative. Gasp! Can't have that! Since Mrs. Palin came to their attention, they have been mercilessly attacking her in any and every way possible. It doesn't matter how ridiculous, how unsubstantiated an allegation may be, they'll run with it. It doesn't matter how low, insulting, or personal it may be, they'll stoop to it. It doesn't matter how much the attack goes against everything they've been claiming to stand for. ie. pretty much the opposite of the MSM's treatment of obama -- they wouldn't criticize him if he sacrificed a virgin on the steps of the White House. It'd be some quaint Kenyan ritual to promote inter-cultural understanding. :-/
The only thing the left has done more fanatically than attack Mrs. Palin has been to idiotically blame former President Bush for just about everything. Probably, somewhere, there's some loon that thinks it is "Bush's fault" that we even have Mrs. Palin. :-) The only good thing that has come out of either of these tendencies is that the left is showing their true colors. They don't really stand behind any issue - they'll drop it, reverse themselves, or sidestep it as the situation dictates. All they are really after is power and control. They want all "the little people" to submit, and they don't care who or what they have to crush to get there.