It breaks my heart when I see URLs with session IDs crawled and indexed by search engines and returned in search results.
The unwitting searcher reads the page title and gets all excited, clicking it in anticipation on landing on
a relevant page for “Toronto ski snowboard shop,” and instead gets this:
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The tragedy is this is completely preventable. Both Google and Yahoo allow you to restrict crawling of session IDs through their webmaster tools. Google’s Vanessa Fox has an amazing explanation of the different options you have for handling this duplicate content problem, including the pros and cons of the meta canonical attribute, 301 redirects and the newest tool, “parameter handling.”
Yahoo also explains how to restrict parameters through its Site Explorer tool, although this may be a short-lived solution for the Yahoo search engine if Yahoo eventually returns results powered by Bing.
I suggest you take a look at this before the next holiday rush to avoid flushing your “free” SEO traffic down the drain.