This arrived last friday, it's great. The steam controller is amazing, but you wil have to put a lot of time into it. It is not a pick up an play kind of thing at the moment. Might improve over time as developers are adapting the controller. One of the best uses is in 'Portal 2', or so they say (haven't tried it yet), since it is the first and only game to native support the controller. The steam link is an interesting little device, it is in fact nothing more then a chromecast with more options to connect HID devices. It mirrors the screen of your steam machine (or a pc running steam) and nothing else. Your steam machine is not free for use by others when you play on it with through the steam link, something to keep in mind. Also it doesn't work well if both your steam machine and steam link are on wifi. After putting an ethernet in the steam link the streaming was much better. There are still some sound hickups sometimes and some games simply refuse to work (Broderlands 2).
In the meantime, steam link already is being hacked on and you can enable ssh access.