The treatment of querystrings is a controversial topic amongst SEO experts. This should add a bit of insight onto how querystrings really affect SEO.

• If Google and other search engines couldn’t traverse dynamic sites, then huge swaths of the Internet such as online databases, blogs, threaded discussion forums, and e-commerce sites (to name a few) would go unlisted
• Querystrings were frowned on initially by search engines because querystrings could define an infinite number of pages, and the crawler could choke. Google has never had this problem, and querystrings, if managed correctly, can be used successfully on any site.
• Google’s Webmaster Guidelines says not to use “&id=” as a parameter in your URLs, as they don’t include these pages in their index.
• According to Matt Cutts, the number of querystring parameters should be limited to one or two