Upgrade nag screens coming to Windows 8.1
Microsoft took a huge gamble with Windows 8, betting big that touch screens would replace the mouse as the primary way of interacting with the operating system. The company replaced the Start menu with a Start screen, which a LOT of people hated. It was one of the main reasons Microsoft's attempt at reinventing Windows flopped so badly.
With Windows 8.1, the software giant reintroduced the Start menu, and made a number of other changes that made it more acceptable to users, but even so, few people will list that OS among their all-time favorites.