Codeanywhere looks nice! I have been using nitrous.io for a long while, very similar to your product. Having an IDE in the cloud offers a lot of conveniences: large builds without heating up your laptop, easy to try different server setups, makes my chromebook and iPad more useful, etc. Of all the cool tech at Google, one of my favorite things was their web based IDE with very nice integration with Perforce, build systems, etc.

I don't understand the "must be on the Internet" complaint. As someone else said, other online resources are large parts of developer workflows - it has been a long time since I have coded without an Internet connection (perhaps a few times a year on an airplane, but I am happy enough writing (I am also an author) or reading on planes).