It has been suggested to me that using anything other than .html or .htm as web page files extentions may reduce the likelihood of the 'offending' pages being indexed by the major search engines. If a site has nothing but .php3 or .phtml (for example) file extensions, this may put it at a serious disadvantage if prominent search engine placement is important to the client. I know that one can simply give all web page filenames a .html extension and then send the lot through the php parser (regardless of whether the page actually contains any php), but this can raise issues of performance and of incompatability with non-PHP server side includes.

Does anyone else have comments on this subject? Can anyone confirm that indeed a file with .php3 or .phtml extension will not be indexed by some of the major search engines? Has anyone actually gone to the trouble of renaming all their .php file extensions to .html and found a significant improvement in hits? Maybe someone knows of a comparision chart between the main search engines that shows which file extensions they are happy with and those they are not?