In a recent interview with Matt Cutts, senior engineer at Google, the question of whether 301 redirects pass on page rank was addressed. Matt. In the interview itself, Matt said that he was not a 100% sure that 301 redirects pass on all of the link weighting or whether there was some natural decay in page rank, however in a subnote, it confirmed that there is some loss of PR for 301 redirects.

Therefore, if you are migrating sites from one domain to another, then in addition to using 301 redirection, you should also look at getting the linking pages updated to reflect the new url, either by emailing the webmaster, changing the signiture of your blog or by creating new links to the new domain name to improve the new domain's link profile.