The Chromecast got released in the UK on Wednesday and I bought one, in the hopes it will be better than the plethora of other streaming devices I have (Apple TV, Google TV, Xbox 360, PS3). As a side note, the Google TV, specifically this model is the worst peice of equipment I've ever owned.
The Chromecast is really easy to setup; plug in the dongle into an HDMI port, plug in the power cable (either USB or mains) and turn your TV on. Then go to chromecast.com/setup and follow the instructions. I set it up on my Mac so I can't vouch for the Windows setup, but I think it'd be pretty similar. Download and run the companion Mac app, setup your preferred wifi network, let any Chromecast updates run and you're good to go. None of the setup is done on the Chromecast itself, so there's no bullshit of trying to put in your wifi password with an on screen keyboard.
Google lists a number of apps on the Chromecast site that have support for the Chromecast but the ones I am most interested in were BBC iPlayer, Netflix, Plex and YouTube. If you've ever used AirPlay on an iOS device, using Chromecast is just as simple. In any supported app, select the "cast button", choose your Chromecast from the list and the video will start playing through your TV.
YouTube, Netflix and BBC iPlayer were fairly straight forward and worked without a hitch. Plex required me to update the server on my Mac to the latest version (I hadn't updated it for over a year). You can also use the Chromecast within Chrome on the desktop by installing the Chromecast extension.
One of the biggest advantages of Chromecast over AirPlay to an Apple TV is the ability to leave the app your streaming from and do other things. When AirPlaying video, the app your streaming from has to be open the whole time, whereas the Chromecast loads the stream to the device itself, allowing you to check Twitter, Facebook or whatever else you want to do.
If you use any of the apps listed on the Chromecast site on a regular basis, for £30 you really can't go wrong.