(1) I don't want my $ to subsidize a company whose business practices appear to be at odds with my own views on ethics
(2) Windows is damned expensive for functional (read pro) versions. I can get huge amounts of functionality from Linux for $100 (really $30 if I don't need to run a server - this means the "personal" version of whatever distribution I choose) - Windows can't touch this price for even the base OS, let alone any useful apps.