Support for power, sleep and wake buttons?

These keys are on 107-key keyboards. Very handy. I guess it needs APM to work.

Is support for it planned?

There is information on BeShare about getting such keyboards to work properly. Also, there are drivers and whatnot on BeBits for multimedia keys as well as a Hex Key Code Finder to help you make your own maps.
Short story is, you enable the keys, find the key code and create an entry in SpicyKeys for what you want it to do. I have a Logitech Schmancy Keyboard and I love controlling SoundPlay and launching applications with it. I think it is way better than using it in Windows.