Google has confirmed that that 301 redirects will cause a tiny loss of Google juice and Pagerank as Google crawls across to the new page. In general, site owners and webmasters believe that 301 redirects are the best way to pass same pagerank, but be aware that some loss will occur in your SEO efforts.
301 Redirects Lose Pagerank
Watch this embedded video where Google engineer Matt Cutts explains clearly that though 301 redirects are the best way to inform search engines that the site has moved to a new url, a ‘very tiny little bit’ of google juice and pagerank drop is inevitable…
Why lose Google juice? He explains the reason very well – because otherwise people might start using 301 redirects instead of direct links to the sites. This ensures that 301 redirects are used only when required.