Hmmm... this is food for thought from Ugo:
File extensions in URLs considered harmful
Russell [Warning: I'm linking to Russell's home page since the permalink seems to be broken] seems to be happy with finally having managed to add an .html extension to his URLs.
I wonder why? What's the point of having extensions in URLs? What if someday you adopt a system whereby you can serve your content in different formats (HTML, WML, RSS, PDF, etc.) to different devices or users based on the User-Agent HTTP header? And all from the same URL? Would it still make sense to use the .html extension?
And what if, a few years from now, HTML is considered obsolete?
This isn't something I thought of before. I was just trying to make it a "normal url" which didn't seem like a dynamic page so that Google would cache the pages. I did notice that Roller's new URLs don't have extensions and will get cached by Google all the same (it'll assume that each non-extension is a directory with a default document). Hmmm...
I hate to limit myself, but then again, I hate to add features that may or may not ever appear... File extensions (as shown by OSX) will be here for a long while yet.