Provide 1st class support in Routing for content-negotiation (Accept:) with appropriate fallback
Many sites, especially enterprise sites, have pages which display data, but also allow that data to be downloaded as CSV, Excel, RTF, PDF, etc.
I feel dirty implementing different URLs for each of these content types when HTTP provides content negotiation support in the form of the Accept header.
ASP.net Routing should provide 1st class support for content negotiation and appropriate fallback (query string) support until the current "work in progress" support for Accept in popular browsers is completed.
If it helps, ExpressJS (running on nodejs) supports content-negotiation in routing.