301 Redirects
All redirects are not created equal.
According to the good ole HTTP 1.1 spec there are a few different types of redirect. Everything from suggesting you view from a different source (303) to insisting that the browser use a proxy server to access the content (305).
While the type of redirect you choose to use doesn’t really matter much to the client (either way they get where they need to go), it can make a difference to the search engines. The general theory is that a temporary redirect will not transfer the pagerank (or incomming link weight) to the target page as effectively as a permanent redirect.
So, what one is the best? Well, a 301 redirect (Moved Permanently) has been suggested as being the way to go. And thankfully implementing it is a sinch (well in PHP at least).
< ?php
header("HTTP/1.1 301 Moved Permanently");
header("Location: http://my.new.location/");
?>
In theory this should transfer all of the page rank weight to the new location and allow the search engine to overlook the redirect page in the future.
This is handy if you have your home page in a sub-directory (like my site) and should be the next best thing to having everything your webroot.