Some SEO experts are talking about canonical URLs specially Matt Cutts.. * But what are these by the way? * What will be its impact on SEO campaigns? * Does all search engines recognize canonical URLs?
A canonical url is your preferred version - technically it should be the url in it's simplest form. Content Management systems have a tendency to produce more than one url for a page - this is a problem for a couple of reasons - firstly, because to a search engine it look like duplicate content, so it will start filtering out urls from serps, and the filtered out urls may not be the ones you want filtered , and secondly because both your internal linking may be linking to more than one version of a page (again, cms are to blame for this), and human beings will c&p the url as it appears in their browser to post in socialbookmarking, blogs etc.and if there are multiple urls for what is really one page, you're dissipating the benefit of those backlinks.
Magda is correct... Canonical URLs are very important. IMO, it's the FIRST thing every webmaster should do when optimizing a new or existing site. Implement URL canonicalization rules using 301 redirects. Read more about URL canonicalization issues and redirecting web pages w/ 301 redirects if you don't fully understand them and why they are important to SEO. NOTE: I would ONLY resort to the <link rel="canonical"> element if you have absolutely no way to implement 301 redirects. This relatively new element is ONLY supported by Google at the moment even though Yahoo! and MS both said over a year and half ago that they were going to support it (don't hold your breathe).