My soon-to-be father in-law asked me what I thought the future of computing would look like. Quantum computers? Holographic storage? HAL 9000? Sure those things could happen, but the only thing I would be willing to bet money on happening would be the rise of Web-based OSs. The reason being is simple: simple is always better than complex if the functionality is the same.
What I mean by that is that as the web continues to evolve and grow in terms of rich, dynamic content it will eventual rival desktop 'thick clients'. When that day comes, it will be much simpler to compute anywhere, on any device, rather than be teathered to your PC. Do you have to work from your desktop at the office? What if you are at home? At a mall kiosk? At a friend's house? On your cell?
I'll avoid making any bold assertions or claims for now, but I am definitely curious on where our data is stored as computers get more connected and the web gets 'good enough' as a platform.
For you pedants out there: Yes, any Web-based application can not be a general purpose operationg system; but I will refer to a specific class of applications as such for the sake of simplicity.