Up with which I will not PUT
For Drupal 8, we want to bake REST support directly into the core system. It's unclear if we'll be able to go full-on hypermedia by the time we ship, but it should be possible to add via contributed modules. For the base system, though, we want to at least follow REST/HTTP semantics properly.
One area we have questions about is PUT, in particular the details of its idempotence requirements. For that reason, I'm reaching out to the Interwebs to see what the consensus is. Details below.