

First of all, if Palin did have a boob job, who cares? Good for her. Although if she did, she does herself no good by lying about it. As to what the truth is here, there does seems to be quite the contrast between the older and newer pictures (perhaps the person in the first photo is a fake Palin like the one from the Nailin' Palin video?). That said, different T-shirts can certainly make a lady's mammalian protuberances look very different size-wise from one shirt to the next. So I'm not passing any judgment. I'll leave it to you to decide.
http://www.huffingtonpost.com/2010/06/12/sarah-palins-boob-gate-re_n_610136.html
http://popwatch.ew.com/2010/06/12/sarah-palins-boobs-are-real-get-over-it/
http://www.gather.com/viewArticle.action?articleId=281474978289538