Well, Windows Phone has been using the name Cortana for their Siri-equivalent. The codename for the next version of IE is reportedly Spartan[1], which is used in Halo. The codename for the upcoming version of Windows is Threshold[2], which again is a name that shows up in Halo. Naming everything after things in Halo is apparently Microsoft's new thing.

1) http://www.zdnet.com/how-the-next-version-of-ie-codenamed-sp... 2) http://www.geek.com/games/microsoft-taps-the-halo-franchise-...