Upgraded my gaming PC, and lost most of the desktop programs on my start menu (was using Classic Shell). Tried re-installing the likes of Steam, Uplay, Origin etc and none of them reappeared. Search/cortana couldn't find them either.
Pin to Start also didn't work, so I basically couldn't re-instate any of my desktop programs on the "new" start menu (which is effectively just a mini version of the Win8 start screen, with reduced functionality if that's possible).
So, I ended up installing Classic Shell, and everything re-appeared. Doesn't say much for Windows 10 though, as that was really the only obvious improvement over Win8. "Upgrade to get your start menu back". They couldn't even do that right.
Let's hope DX12 lives up to the hype.