Don't use session IDs

Like dynamic URLs, search engines don't tend to like URLs with session IDs on them. In fact, session IDs seem to cause even more problems with search engine spiders than plain dynamic URLs. The problem is that every time the spider comes to a site with session IDs it can index that site as a completely new URL - even though the content is identical. This can lead to the search engine thinking you are trying to spam them with identical content, and could even get your site banned if it got bad enough. Google guidelines now state that id= URL parameters are okay, but that doesn't mean that other search engines won't choke on them.