Google have just updated their guidelines in regards to rewriting URLs.

Previously, the guideline stated:

"Don't use "&id=" as a parameter in your URLs, as we don't include these pages in our index"

Google have now removed this guideline, saying they can now index URLs that contain that parameter. Google have also posted a blog entry explaining the difference between dynamic URL's and static URL's, and encourage you to let Google handle the problem.

Should You Avoid Rewriting Dynamic URLs?

In most cases, yes. The translation can be messy, and if not handled correctly can lead to indexing problems.

However, for SEO purposes you might want to consider the following points.

Sometimes Static URLs Do Make For Better SEO

• The URLs look nicer and will likely get clicked on more often
• The URLs will provide better anchor text if people use the URLs as the link anchor text
• If you later change CMS programs having core clean URLs associated with content make it easier to mesh that content with the new CMS
  the benefit Google espouses for dynamic URLs (Googlebot being able to stab more random search attempts into a search box) is only beneficial if your site structure is poor and/or you have way more pagerank than content (like a wikipedia or techcrunch)