Changing Pages and Domains
Occassionally a logisitical issue such as a site changing domain names can pop up and threaten to destroy months or even years of careful search engine optimization. There is hope, however, in the form of a 301 redirect. When used, a 301 redirect sends the message that a page or site has permanently changed addresses, and all links inbound to that location should now point to the new location.
Use of a 301 redirect has many advantages for optimization efforts. Firstly, it preserves ranking between transitions. Secondly, it transfers PageRank to the new page. For all intents and purposes, the search engines consider it the same page or site with a different URL. The only downside is that owners of links that point to the previous address will need to be contacted and asked to change their links to the new address. This may take some legwork, but in the end is more than worthwhile.
It should be noted that using a 301 redirect from an existing page to another page that already enjoys inbound links and PageRank contributes in an additive fashion. However, use of this should tactic should be limited to legitimate page movements, as overuse may cause the search engines to penalize or blacklist your site.