Came across an interesting write-up by Tim Berners Lee titled "Cool URLs dont' change", and found many more interesting mistakes we do while writing web application and designing the architecture. We normally design the web sites with Dirty URLs by-default (in most of the cases).
e.g. My profile at Microsoft can be reached if you can type
Dirty URLs Complex, hard-to-read URLs are often dubbed dirty URLs because they tend to be littered with punctuation and identifiers that are at best irrelevant to the ordinary user. URLs such as http://www.example.com/cgi-bin/gen.pl?id=4&view=basic are commonplace in today's dynamic Web. Unfortunately, dirty URLs have a variety of troubling aspects, including:
01. Dirty URLs are difficult to type. 02. Dirty URLs do not promote usability. 03. Dirty URLs are a security risk. 04. Dirty URLs impede abstraction and maintainability.