>Scott Hanselman famously said “URLs are UI”

I actually implemented a comment system where users just pick any arbitrary URL on the domain, ie, http://exampledomain.com/, and append /@say/ to the URL along with their comment so the URL is the UI. An example comment would be typed in the URL bar like,

http://exampledomain.com/somefolder/somepage.html/@say/Hey! Cool somepage. - Me

And then my perl script tailing the webserver log file sees the line and and adds the comment "Hey! Cool somepage. - Me" to the .html file on disk for comments.