Google has a record of planning well ahead and doing things right with big picture in mind. Factor aside that it may become a Big Brother, the convergence of services it has in mind is fantastic. In addition to already good Google Docs, email and other web based services, now it has a fantastic telefony in hand in result of aquisition of GrandCentral. You can have your own free telephone number and be in communication with the entire world without any more need for telephone company...
More and more people and companies start using Google Docs, instead of Office, etc. , etc...
To complement integration of all these services Google needs an independent OS to connect to all these services. Whether it is netbooks or any other PC's.
Personal Virtual PCs on the Internet will start working and be appreciated more and more in the future. Just imagine: how many times we lost some important files because our hard disk crashed and we did not back up on time? With Virtual Computer on the web, it would not be lost, it is safely where you stored it, backed up and updated...