Kurt Cagle today published an article on DevX.com: "From Social to Serious: Combining Twitter and RESTful Web Services". Using the implementation of a twitter reader as an example, the article demonstrates how to build a RESTful data application. It covers many topics along the way, including request routing and XProc.
Note: if you are using the trunk version of eXist, you may want to look at XQueryURLRewrite, which is the successor of the RedirectorServlet used by Kurt.