I had buy Minecraft this December, and I've had problems with servers and in single player world. Just imagine, I'm playing Minecraft in the Nether and then my Minecraft crashes, but when the game finished in the development console says this:

"Can't keep up! Did the system time change, or is the server overloaded? Running 5381ms behind, skipping 107 tick(s)
[21:05:16 INFO]: Client> [21:05:16] [Server thread/INFO]: Saving and pausing game...
[21:05:16 INFO]: Client> [21:05:16] [Server thread/INFO]: Saving chunks for level 'Supervivencia'/Overworld
[21:05:16 INFO]: Client> [21:05:16] [Server thread/INFO]: Saving chunks for level 'Supervivencia'/Nether
[21:05:16 INFO]: Client> [21:05:16] [Server thread/INFO]: Saving chunks for level 'Supervivencia'/The End
[21:06:28 INFO]: Client> [21:06:28] [Server thread/INFO]: Saving and pausing game...
[21:06:28 INFO]: Client> [21:06:28] [Server thread/INFO]: Saving chunks for level 'Supervivencia'/Overworld
[21:06:29 INFO]: Client> [21:06:29] [Server thread/INFO]: Saving chunks for level 'Supervivencia'/Nether
[21:06:29 INFO]: Client> [21:06:29] [Server thread/INFO]: Saving chunks for level 'Supervivencia'/The End
[21:10:22 ERROR]: Game ended with bad state (exit code -805306369)
[21:10:22 INFO]: Deleting C:\Users____\AppData\Roaming\.minecraft\versions\1.7.4\1.7.4-natives-2355186615559
[21:10:22 INFO]: Ignoring visibility rule and showing launcher due to a game crash
[21:10:22 WARN]: Couldn't delete C:\Users____\AppData\Roaming\.minecraft\versions\1.7.4\1.7.4-natives-2355186615559 - scheduling for deletion upon exit