For all of the Windows-related debacles, Vista was by far the worst for Microsoft.
Vista was released in 2007 to much fanfare, since it was the first new operating system that Microsoft had unveiled since XP in 2001.
But that's where the excitement ended. Vista was plagued by bugs, software and hardware incompatibilities, sluggishness and annoying security alerts (to name a few common complaints).
The operating system was so badly received that the majority of businesses opted to stick with the eight-year-old Windows XP rather than upgrade. XP still has four times as many users as Microsoft Vista.
Rival Apple cashed in on Vista's annoyances with its popular "Mac vs. PC" ad campaign. One featured a Secret Service guard asking PC if he would like to cancel or allow any comment he made on Vista's security alerts. Since Vista's release, Macintosh's market share nearly doubled.
But there were less tangible effects of Vista, including a loss of Microsoft's credibility with consumers. Many experts think consumers will hold off their purchases of Windows 7, which debuts Oct. 22, until the operating system has been sufficiently tested.