Ubuntu has the momentum to become the de-facto operating system for some. Ubuntu just needs more time to mature for the majority.
Read tha paper on it here
It is a matter of time before Linux becomes more widely used but Im afraid that it is just not yet. Computer users demand to play games and almost all games are made for Windows. Businesses require usage of Windows only software and often cannot afford to train employees on new computer systems. Grandmas of the world would still be in a state of confusion with Linux systems.