This link is an open thread in Facebook @ Ubuntu.
My personal impression after reading the multi page thread is that most people who posted their reason for not using Windows is Microsoft. They do not want to spend so much money for a product that does not satisfy their needs anymore. They don’t want to be in a situation where they are restricted to use their computers.
In this tough times, people are searching for ways to cut costs and still be able to connect to their loved ones, do their jobs at home and do stuff online.
Ubuntu and Linux developers have worked hard to improve several distributions of linux to the level that they can offer them as alternatives to Microsoft’s wares.