An interesting post - but I don't think reactive design is a must for best practices based on this article from Google:
http://googlewebmastercentral.blogspot. ... obile.htmlSeems like Google is okay with figuring out that a mobile version of a page should be served to mobile visitors and will dynamically replace the regular URL with the mobile one for results.
Article also misses out on rel="alternate" microdata for specifying alternate media type page locations. See
http://microformats.org/wiki/rel-alternateThat being said, reactive design is the hot new thing in web design - if you can serve the same content optimized for all different media types in one place you're probably going to get some of the best benefit, but it's rather harder to implement than just redirects for mobile devices.