I'm a big fan of open source and Linux...Never touching IE again. Mozilla all the way.
However, releasing the source of windows would be just plain stupid. First off, thousands of loopholes would be discovered, destroying what little security windows has. It would be a disaster for the majority of the world, who so whole-heartedly rely on the system. Releasing the code would mean pretty much no more safe computing for 90% of the world, at least for a year or two. For microsoft, it would spell disaster. Not that I care about what happens to microsoft, but out of the sympothy for those who would get their computer fucked up, i think it would be a bad decision.