Last month, the search engines agreed together to support a new URL canonicalization standard to avoid some duplicate content issues. It allows you to label varying versions of the same url with the canonical URL in the head of the page, that you really want indexed
For example –
<link rel=”canonical” href=”http://www.mydomain.com/my/canonical/url” />
Search engines have said that they plan to treat this tag similar to a 301 redirect, but keep in mind that it only works within a single site, and not from one domain name to the next. Here’s a Matt Cutts video about the change that took place, and was announced at SMX West.