I've given a lot of thought, lately, to the famous Cool URIs don't change W3C document. Should URLs end in a slash or not? Should they end in a file-extension or not? (What if you're serving multiple formats of the same document?)
I've been using a trailing slash (for, admittedly, no defensible reason: the Django guys do it, and they're cool). A trailing slash implies a directory, which doesn't apply to serving a document--unless you think of it as a directory containing that document in a variety of formats.
Which brings us to the file extension dilemma. It seems appropriate to serve differing formats for differing extensions (e.g. HTML, PDF, XML, JSON); but, perhaps it's best to keep the URL generic and rely on the "Accept" field in the request header to decide on the best output format.
Certainly not many tools support this kind of respect for HTTP headers, but I'm starting to believe that fully embracing HTTP is The Right Thing (TM), and it's the direction the industry is (slowly) moving toward. (REST!)
Incidentally, screw the W3C for not including PUT and DELETE in HTML. Oh, and HTTP authentication needs some serious work. /EORant