FYI. I've had sleep issues since installing the Jan 14th patches on my SP2 (4300u). It has stopped "idle" sleeping, meaning after the set amount of time in the Power plan's sleep setting has passed, it won't sleep. It will go to sleep fine if I close the Type Cover, push the power button, run the battery down etc. Checking the event log confirms this. After trial and error I've determined that putting the device in Airport mode fixes the symptom and will allow it to "idle" sleep on its own. Not sure what was in the patches that triggered this issue with the network/radio infrastructure (as who knows where the problem really lies). What makes the "idle" timer different than the other triggers in this case I'm not sure. I believe it's much easier to preempt it in general. Just a heads up for people if they run into this. Edit: Looks like it doesn't have to be in Airport mode, turning off Wi-Fi alone will allow "System idle" sleep to function.