The only advantage of using mod_rewrite to change your URLs for SEO is that you can remove unnecessary clutter and make sure your keywords are prominent in your URL. This will have a small direct effect on your rankings. Indirectly this will also help you with SEO as it will encourage other webmasters to link to your site with those keywords in their link as many use the URL to help formulate their anchor text.
Otherwise there is no harm in using dynamic URLs or having query string in your URL from an SEO point of view.
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He's No Good To Me Dead
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since May 2006