I've had this happen to me about 5 times in the past few weeks. I can't recreate it in any way, but when it does happen it will just sit at a black screen till i hit the home button again. It acts like the screen was on though, so when i hit the home button when its on the black screen it will slide left to the search screen. Just wondering if maybe i'm trying to unlock it way too fast or something. Or if anyone else has experienced this yet. Oh and i'm on a 4s running 5.1.