Being a fan of Apache, I've read the modrewrite guide a few times. Its very cool stuff, and allows you to do almost anything you want with URLs. If you've interacted with the rewriting capabilities of modrewrite, you know its raw power, and sometimes its capacity is overkill, and something more flexible is required.
Therein lies the concept of url routing. I'm not a fan of that name at all. Routing to me means defining connections between separate networks, but the name has stuck.
Frameworks that use Routing
Ruby on Rails and Symfony are two that I'm aware of, and I'm sure that there are many more. What I do like about the way they manage the routing specifications - in a configuration file. Symfony uses YAML, and while I prefer XML, the idea is the similar enough to give me a sense of like-mindedness.
Downfalls of Routing
Sometimes routing can actually obfuscate what's going on, that's why a lot of times I like to keep the url as the default query string parameters that are used by browsers and web servers by default on private applications.
Benefits of Routing
However, when it comes to public resources, the url can serve as another preview for users to see before visiting a website.
Routing with XSL
XSL isn't really designed for routing as far as I can tell, but it is possible to integrate a routing process into an XSL framework, like Nexista