Sometimes when you do a site redesign or a company rebranding, you also change your domain name. But sometimes publishers are simply changing the domain name, and everything else (except for perhaps branding changes) stays the same.
One of the more challenging aspects of a domain name switchover is the potential loss of trust the search engines attached to the old domain. The trust does not always shift that easily to the new domain when you make the move. Another issue is that the keywords present in the old domain name but not in the new domain name may negatively impact for search terms that include the keyword. For example, when Matt Mullenweg, founder of WordPress, switched domains on his personal site from http://photomatt.net to http://ma.tt, his position in Google for Matt dropped out of the #1 spot.
One danger is that the new domain may go through a scenario where the newness of the domain acts as a damper on the site’s rankings. In other words, the site relevance and inbound link profile may suggest a high ranking for some search queries, but because the site is not trusted yet, the rankings are suppressed, and traffic is much lower than it would otherwise be.
This is one reason for the recommendation we will make in the upcoming best practices list to get the most important links to your old domain switched over to your new domain. One other tactic you can try ...