I use my PC *only* for playing games, whichever OS they make, please dont make it hard for game devs to code cool games.... it'd be hard to imagine them to need to support another library (like Open GL/Direct X).
On a separate thought... An online OS might not be easy to adopt in third world countries where Internet is still considered a luxury. Its a neat idea though, no need to have CDs to scratch and replace..., possibility of using something like Steam technology and piracy would be very much controlled.