Re: VM
> Another VM just sounds like JVM, Flash, Silverlight etc and will end up with the same problems.
There is a difference. If it also compiles to javascript, then you only write once and just load either dart or JS into the browser an request. The VM's mentioned above have platform limitations.
Google has enough of the browser market via chrome and (more importantly) android to make this work. This might make web apps (which are horrid enough on a pc) work faster so mobile devices can run them.
As long as it compiles properly to JS as well, google can afford to go it alone. If gmail runs faster under chrome than anything else, so be it, hotmail doesn't need to come along for the ride. You might eat more memory running a JS VM and a Dart VM, but memory is cheap.
The aim of dart/NaCl etc is to get web apps running at a decent speed to bypass MS' grip on the desktop.