Mark Pilgrim has a long explanatio about making cruft-free URLs in which he goes through a lot of steps to remove the .html file extension in URLS, so a URL that looked like http://…/xp.html would be shortened to http://…/xp
Yuck. I agree with this comment that file extensions are generally useful information,
As an end user, I sometimes derive assurance in knowing what kind of file I am clicking on and going to view. The removal of the “.html” extension removes that.