Sleep/wake fix
I fixed this by resetting my SMC:
Shut down the computer.
Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
Release all the keys and the power button at the same time.
Press the power button to turn on the computer.
This worked for me. You could also reset the NVRAM if this doesn't solve it, but most forums suggest resetting the SMC does the trick.