NYT says 30 minutes ago, and I guess they're right and now I will forget about it:

"So in the end, this could simply be one of those it-is-what-it-is moments. Ms. Palin was weary of being governor, and, facing constant ethics complaints, she saw her family being chewed up by bad publicity and decided to trade those things for the opportunity to work on her book (for which she received a lucrative contract), tour the country giving paid speeches and consider offers from television or radio to become a highly paid commentator. . . .

From this perspective, the decision was simple and sensible: Less stress, and more national attention and money."