No. HTML5/web/cloud/SaaS/whatever is a networked interaction-, multimedia- and cross-platform interface. It's like X11+audio.
It has to run on a... You know; actual computer, hmkay?
So it is an addition to computing and certainly will not replace anything. The only possible outcome might be running a server at home, with networked terminals for both the homeserver and remote servers. They call this a "hybrid-cloud" environment.
Thanks, but no thanks. It's nice for mobile, but I will _never_ ditch the desktop, _ever_.
In windowed mode it shows decent performance on HD5750 with opensource radeon drivers. And dang, scene itself looks pretty impressive, it's even hard to believe it's pure HTML+JS (even if backed by serious 3D engine).