I don't know a whole lot about her but it seems like because Palin represents conservatism and is a woman that is reason enough to make them angry and scared. Why are they scared? They are scared because they see the Republican party being "progressive" and having a woman on their ticket, something they couldn't achieve. They're afraid that the so called moderates will "fall" for this trick and are indignant about it.
So they don't really dislike her so much as they dislike what she represents (not that they like her). It is truly awful that anyone would be so venomous against someone just for political gain. So they dig up everything they can and try to make Palin seem like a religious nut or a political nut or they call her and her family names. To her credit though she is largely ignoring these people and these games and in so doing continues to draw big crowds and supporters.
The one thing that stands out in these attacks is how liberals and those in the media try to tell us she's not conservative enough. It's funny because people who know nothing about conservatism try to tell conservatives what is and isn't conservative. I hear the same kind of stuff on my ChristianPolitics blog, people trying to tell me what "my" religion is really all about. When they can't really talk about something or someone on the merits, they either try to get you to doubt yourself or just call you names, it really shows how unskilled they are at debating.