Hm...if my Playbook is in standby, I get no notification of messages through bridged device. If the screen is on I get the red corner of course, but if it's not on, then there's nothing. Why doesn't the LED notification work?
better yet your palybook is probably not sleeping unless you used your filed down finger tip to sleep it with the hard power button. Who knew Steve Jobs was talking about the Power Button not using the device for surfing.