Roy, you are correct on about everything you said. Chromecast like any streaming devise can eat you alive if you use it to stream movies on a metered internet connection. Currently you can view anything that you can view on the Chrome browser on Windows 7 or up. It also works on IOS but I can't tell you what version off the top off my head. It will also work through an app for Android or Apple devises.
Currently there are 10 apps that work through Chromecast so there definitely is a limited number of applications at this time. There will be more to come I am certain of that. For $35 I couldn't buy an HDMI cable to run my laptop from my recliner to the TV.
For Christmas, I wanted the in-laws to be able to experience the rest of the family they couldn't travel to see. By having everyone feed the videos and pictures to me through Facebook I knew I could seamlessly play them all one after the other with limited interruption. It won't be for everyone, but I will not be giving mine up.