I saw some recent analysis in a serious blog (I don't remember where it was, but I'll try to find the link) which said that Sarah Palin is pro-immigration. That is she becomes a president, she will do exactly the same thing as McCain - give amnesty to tens of millions of illegals. This claim about her was based on her interviews and her answers to direct questions about illegal immigrants.
Now, in my book, this is one of the most serious accusation. It is #2 after being anti-Israel. It might even have the same priority, depending how you look at it.