Windows 3.x introduced the "Blue Screen of Death" to an ungrateful nation. Windows ME was such a dog it came with its own fleas. (We won't even discuss Microsoft Bob.) But for our money, the worst Windows version of all time is Vista. Years overdue, stripped of virtually all the ground-breaking features it was supposed to have, Vista was a wet hot mess that was only made worse by the over-the-top hype accompanying its release. Compatibility snafus, performance problems, and impossibly annoying User Account Controls doomed it from the start. Even Microsoft's core constituency, enterprise geeks, stayed away in droves. The company got sued for letting hardware manufacturers label their systems "Vista Ready" when they were anything but. Then again, nobody was ready for Vista -- including Microsoft.
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Image: flickr/Amio Cajander