Windows 10 64 bit, Windows 8 64 bit
Broken: 2.76b f337fea
Short description of error
Former versions of Blender created the registry node "HKLM/Software/BlenderFoundation" with key "Install_Dir" in it. The node is not created with version 2.76b any longer; neither by Blender's 64 nor the 32 bit version. Bad for me because my add-on's installer cannot find Blender's "addons" directory, and the user has to copy the script by hand now.
Exact steps for others to reproduce the error
Uninstall your current Blender, double click on "blender-2.76b-windows32.msi" or "blender-2.76b-windows64.msi" and check the Windows registry for the node "HKLM/Software/BlenderFoundation". It is not there.