Since all of these compile down to javascript, they all suffer from at least some limitations of javascript -- the main one being performance. Yes, all browser manufacturers are trying to make it as fast as they can, but I sincerely doubt I will see the day javascript can run as fast as a statically typed and (jit) compiled language that isn't being executed by the browser. And when I say that, I don't mean little synthetic scenarios where some piece of javascript manages to be faster than something gcc spit out. I've already seen those, and they don't impress me any more so than a hummer being able to look like a ferrari if you get the angle and lights just right.

I'm a fan of P/NaCl for this reason. Their approach goes directly at the problem instead of banging on a square peg for years and years until it barely manages to fit through a round hole. By the way, that is the only way I can describe using html/js/css for application development at this point. If it makes me sound bitter/angry, it's probably because I've been doing it for too long and grown tired of how tedious and limited it is.