Bought 2 via relatives in Tucson, Arizona. Works well on every LG and Samsung TV we've tried, but has an issue on our old Toshiba Regza 37X3030DB where switching HDMI ports (to watch SkyHD) and back leaves us with a nominally working device, but blue screen and no audio. Cycling the power on the Chromecast after switching HDMI channels fixes it. Reported that back to Google (their help web page cleverly attaches a log file from the device automatically).
That said, works brilliantly, even showing HD video from YouTube and Netflix over our crappy, 3 miles from the BT Exchange, 1.3Mb/s "Broadband".
Waiting for the Chromecast API to be released, at which point there should be a deluge of other apps coming out. I've heard somewhere that Google anticipate being north of 13 million sold by the end of the year, which would take them past the complete installed base numbers for Apple TV. I guess they may also be close to overtaking Kinect as the fastest growth from launch to 10 million units shipped of any consumer electronics device.
So, another Google Moonshot executing nicely. Just need to get them shipping outside the USA now!