Carl Zimmer has a new book coming out in November on human evolution. Carl also has a magisterial post up on the recent completion of a draft of the chimpanzee genome (a paper is due to go up on the Nature website at some point). You can connect the dots on why this important, but Carl goes through the play-by-play. Please note that the paper which analyzed gene expression differences in chimpanzee and human brains had to take into the account the fact that the sequence draft they had access to for chimps was filled with errors, not the greatest when you are probably looking for small differences that can lead to large effects.
Erratum: From the comments, “…major problem for studying gene expression changes is that it is done on arrays with probes based on human sequences. Now that we have the chimp genome, we can use this to igore array signals from probes that cover DNA where humans and chimps differ. Errors in the chimp sequence draft have little impact on this analysis.”