I couldn't wait, using the HDMI cable or the xbox that sounds like ten hair dryers was getting old so I bought a import from amazon for £34. It arrived pretty quickly even using the free delivery. Not going to do a unboxing or any other type of weird techo fetish stuff. Just some observations from using it for a few days.
Only netflix, youtube, google video currently offer native support from within chrome or through apps and they all run in full HD and the video and sound is pretty amazing considering the hardware. Casting from tablet or phone is better because it runs in the notifications tray and it becomes your remote and you can let the screen lock/go to sleep. In chrome on the pc once you cast, the computer has to keep running and the tab open otherwise netflix/youtube stop casting.
You can stream your own videos by opening them in Chrome (Ctrl + O) but it won't play avi videos it starts downloading them from the source folder to its own download folder for some reason, mp4 seems to work ok though, use "any video converter" or something similar to convert them. But to be honest, it isn't that great streaming video from a chrome tab, the cpu usage is high, the video chopping and your processor fan will be annoyingly loud unless you pc is nippy and quiet. If your TV has a usb slot it probably will play the avi's if you stick them on your usb stick anyway, mine is a cheap tv and it does.
Sites with flash video seems to work better, you can start the video, full screen it and then Alt + Tab to get to the browser again and do other stuff, this also works with iplayer and is ok. Obviously native support and apps would be better as you have to leave the tab open and computer running.
The other thing I noticed is you can use the spotify web player, but if you cast the tab at its highest bitrate its choppy. I casted the tab as 480 and the sound improved dramatically and was smooth as butter.
You can cast your entire screen but it chops a bit off if your screen dimensions don't match. Its probably ok for power point stuff though, I cannot see it for anything else at the minute. I tried casting a full screen with a ps2 game running under emulation. It was horrendously slow, mostly because my laptop is slow running the ps2 emulator anyway but I think there is so much potential, imagine casting a snes emulator from your nexus 7 so you can have a blast of Mario Kart (providing you legally own the game obv) or even if games were written to run natively, Order and Chaos online is a basic MMO that has a browser version, there are lots of other games written these days that run under flash they would work well with some tweaking. I think cloud gaming, albeit with simple games is a real possiblity. Once google get their backsides into gear and get people writing stuff I'm sure it will have lots of great things on it that we cannot even think of yet, currently only naughts and crosses exists as a game on google play.
I suspect the UK release is being held up because the BBC are being slow getting their app ready, their android app has always been pants (they went all in with flash the morons) and google want some extra third party stuff to launch with other that Netflix. For £34 quid, even if it only did the things it does now it would be a absolute bargain, I cannot wait to see what people get on there in the future.