Matt Posted This criticism of YouOS that I think misses some key points of why YouOS and it's Open Source competition eyeOS are important and useful. Matt complains about adding two layers of abstraction between the application and the user, but he misses another that make all the difference. Web based operating systems also add the network layer between the system and the end user.
That is the key appeal of Web apps in general, they are accessible from any browser. Networked OS's are as old as UNIX, but networked Gui's usually depend on software that is not universally installed. EyeOS/YouOS is not competing with Windows as a platform, it's competing with with Windows plus Windows Terminal Services plus having a compatible client plus praying it works plus vendor lock in. In that context Web based applications are a clear winner in most cases, and have been for a while.
Another thing I think Matt misses is that these OS's are not tied to JavaScript for anything other than basic window operations. Application back ends run on the server, can be written in any language, and can run at native speeds. If an app needs more graphical power, the front end can use Flash or Java and still tie into the API's for file access. There will be a network bottleneck, but that's inevitable for any remote access solution. Matt is right that JavaScript wasn't made for systems programming, but the only part of Web OS's that is strictly tied to JavaScript is lightweight user interface programming, which is exactly what JavaScript was designed for.