I thought of using this as a crude measure of the popularity of some popular web server technologies. For PHP, combine the url:php, url:phtml and url:php3 numbers.
The advantage of this method is that it better approximates the way Web pages are distributed over the Internet. The disadvantage is that Web pages which are not accessible by Search Engines are not counted (robots.txt and URL’s with query-strings), and some PHP Web pages do not have a php, php3 nor phtml extension.
Visit http://php.weblogs.com/popularity for the full article.