Since the beginning of december (1st) I'm also having this problem.
Phone is on but on lock screen (got glance off) and then when I want to 'unwake' my phone, it doesn't do anything.
I have to soft reset, my phones start up again and then nothing's wrong.
Last two nights it froze (it's on powercable then), because of this my alarm didn't go off twice, so overslept twice already!!
Just now (at work) I tried to unlock my phone and again had to soft reset (didn't respond to anything). while 30min ago everyting was okay.
I really need a solution for this.. is battery saving causing this error? Or some other update?