Scott Mitchell (of 4GuysFromRolla.com) has a cool new article up on MSDN that has a pretty complete and detailed dip into URL Rewriting. An awesome article - Scott really walks you through the entire process. This article will give you everything you need to implement URL Rewriting in your ASP.NET apps.
[URL Rewriting in ASP.NET]
However, that said, Scott Watermasysk, who implemented URL Rewriting in .Text, has become convinced that URL Rewriting is not that important. Mainly because a typical user is usually not going to type in a full URL other than the root domain and he has doubts that meaningful URLs mean anything to the user. While that is partly true and I can't see users typing in a full URL in typical cases, I do like to see meaningful URLs (and I am glad Scott implemented them in .Text). I like to be able to tell what the page topic will likely be by seeing the URL (instead of something with an ID etc). I'll continue to implement URL Rewriting - I like it.