I have used my new iMac 27" for quite some time now and I am quite pleased with it. However, there is one odd thing. When the computer sleep, manually or automatically, I can only wake it up again by pressing the power button on the backside. It will not wake up simply by pressing a mouse button or pressing a key on the keyboard. I have never had this issue with any of my other Macs (Mac Pro, iMac, MacBook Pro). Is anyone else experiencing this? I can not possibly see that this would be by design. Are there any settings somewhere to change it? Or is it a Mountain Lion thing?