How much difference does it make if dynamic URLs of a site were changed to static ones (even it is just seemingly so)? Moreover, what is the changes were to be carried across the site?

We won't have been too wrong if we assumed that considerable risk was involved. However, a study by Search Engine Watch has proved otherwise. Predictably, usability and click through rates should have improved. The surprise element was that the search engines responded positively to the changes in URLs.

Carsten Cumbrowski summarizes the way these URLs were changed. All the dynamic URLs were remapped "via a tools such as mod-rewrite/.htaccess file (Apache Webserver) or Helicon ISAPI Rewrite (Windows IIS Webserver) to static URLs and 301 redirected (Not 302!) all dynamic URLs to the new static looking ones."

The rewrite tool follows certain specified rules. Therefore not much of code change is required. This easy and simple change at least doubled the number of indexed pages in all three search engines. The figures for Google jumped from 38,400 to 62,200, for MSN it went from 597 to 2,068, and for Yahoo! the indexed pages leapt to 30,581 from 10,633. This was when no other changes were made. There are additional resources at the Search Engine Journal post which support these findings.