I know this is a little late.. but I just bought the Apple wireless keyboard. It woks great. The brightness keys work, as do the volume and mute keys. The "eject" looking key in the upper right corner makes the on-screen keyboard appear. Caps lock works. The arrow keys work in some places, like moving around a text box (like the one I'm typing in now). Tab works. The music control keys work.
The ones that don't seem to do anything are the ESC key, the fn, control, option, and command keys. The "show all wondows" and the key next to that, which looks lie a meter of some sort, doesn't do anything.
I'm loving the keyboard. I can type a lot faster and with fewer errors than with the on-screen keyboard. I also don't have to switch to numbers or symbols. Very light weight and thin. Well thought out.