The casting of the entire desktop is an experimental feature. I already see why. While sending my desktop to the Chromecast unit, the connection dropped twice. Tab casting was smooth though.
While I am sure this comments will not make it to the world wide news scene, I simply wanted to make mention of the Chromecast device, since I can see the value to a lot of people.
I actually don't need it, but being the technology addict I am, I just had to get it. Since I have a Google TV (courtesy of Google when they first came out, I applied for a developer sponsored unit, and I got it), an XBox, and my DirectTV set top box also go online, most of the features of the Chromecast were already covered. However, now I can also load up my MacBook Pro screen on the TV without having to use a cable. Unlike the Apple TV, this puppy works with Macs and PCs.
But for those that don't have any online-capable device connected to the bigger screen in the house, the Chromecast is a great alternative. I can also see the benefit of having such a tiny device with me during business trips. You never know when you might need to do an impromptu presentation at the hotel or local bar, and with the Chromecast, it's a piece of cake.
That's all I've got for now.