#2 - Windows Vista

Remember back when Windows Vista, coupled with the Games for Windows platform, was going to be the panacea that would cure what ailed PC gaming and issue in a new “renaissance” for the platform?  It's only been a few years but it may as well have been decades ago for as hollow as that promise turned out to be.  Vista's security measures were highly annoying to certain indie developers, since programs without the right software certificates would often be deleted by the OS.  Vista also had very high system requirements and PC games typically ran slower than they did in Windows XP.  Games for Windows never did lead to the high level of interaction and cross-compatibility with games on Xbox Live, nor did it significantly reduce the issues many users have with PC titles.  The initial subscription charge for Games for Windows - Live was also a big mistake, leaving it chasing other subscription free services on PC like Steam.  Despite initial promises, Vista seems to have only hurt, not helped, PC gaming... but Microsoft promises they'll lead PC gamers to the promised land again with Windows 7, and why would they lie?