Using your Oculus Rift with Steam VR is usually a painless experience, but some people are reporting a bug that essentially ruins a gaming session. In the middle of playing, you will be switched over to a black screen with an hourglass in the middle — the default loading screen for the Rift. The problem: the black loading screen doesn't go away until you restart the game.
There is no official fix from Steam or Oculus, but that doesn't mean the bug can't be avoided. It seems as though being a part of the SteamVR and Steam Beta Update is what's causing the problem, and people who have opted out of the Beta have not seen the bug again.