Finally, someone in the press that can see how groundbreaking this is.
Thanks Neil for understanding just how important Googlecast might be. Too many people (like many of your commenters here) only see this as a way to get video onto your TV. If that is all you think it is then it is easy to think that it does nothing more than Airplay or DLNA and not see what the big deal is.
Many in the press compare it to Roku and ask which should you buy. In reality, Google cast is something that will get incorporated into Roku or your future television.
The correct way to see the potential is to ask yourself for any given app on your smartphone, is there any way that app can be enhanced if the app could control your large television display to display video, audio, text, images, or anything else that you can do in a web page. Certainly when one thinks of Youtube and Netflix it is easy to see that yes these can be greatly enhanced if the video and audio could be played on the television. But the potential goes far beyond this.
An alternative approach is to ask if for any given streaming media content could that content be enhanced by having the interactivity from a secondary smaller touch screen device that has better ways to interact than a clunky remote, including touch capability, audio input, accelerometers, and speech recognition.
To see the full potential requires some imagination and it will take years for developers to come up with new ways to use it that we haven't even thought of yet.
Here are a couple of thoughts off the top of my head. These are probably going to sound lame. If you went back in time 20 years ago and explained to someone at that time some of the top internet properties, you would sound pretty lame as well.
Imagine a shopping app like Zappos. Buying shoes using a little 4 inch screen is a bit sketchy. Imagine if as you browsed shoes the app sent high def video and images of the shoes to your television so you can see what you are buying in greater detail.
Imagine something like taking an online class from your smartphone. It could show the lecture on the big screen and your phone could be used for asking questions or the teacher could ask the students questions that they answer on their phone.
Imagine more interactivity with streaming video content. Say you are watching a live stream of the emmy awards and there is polling on your phone to vote for who you think will win the category and a way to post comments. Or a streaming internet game show that lets you play along with the contestants.
There is lots of potential for casual gaming as well using the display of the big screen and you phone as a controller. You won't have the horsepower to do a first-person shooter, but there are certainly many more casual games that would work.
Certainly many things like these can be sort of be done now using different unconnected apps or relying on expensive hardware like a game box or a full-fledged computer, but not with all the simplicity and tight integration you could get with Googlecast.
When you imagine some of the things that could be done it is easy to see that this is so much more than an Airplay or DLNA copy.
So I think you'll eventually see many things you can do with Googlecast that haven't even been imagined yet. Developers need to time to come up with ways to use it since it is breaking new ground.