Adam Kalsey - Versioning REST:

"One thing I dislike about URL schemes for versioning a web services resource is it feels decidedly un-RESTful. The URL of a resource shouldn’t change simply because the format of that resource’s representation does.

[...] In Tagyu, I’ve going to accomplish this by placing a <versions/> element in the XML file. This element will provide access to the previous, next, and latest resource representations as well as a reference for which one is being used currently. Instead of referring to versions with version numbers, I’m using the date that the version was released, simply because this date has more meaning than an arbitrarily-chosen version number."