Pbbuttonsd
PMU-based laptops can use either pmud (which works, but doesn't have a lot of features—and which, occasionally, is maintained by fellow m68k porter Michael Schmitz) or pbbuttonsd, (which is a lot better) for their power management. Pbbuttonsd also has support for doing stuff with the hotkeys on the apple keyboard, like changing the screen brightness, the sound volume, or going to sleep (if your laptop supports it) after one uses the power button.
In addition, pbbuttonsd will reduce the screen brightness if the laptop is running on battery power and hasn't been used for a while.
This is cool.
Unfortunately, it also does it if I'm using an external USB mouse to browse the web and don't touch my keyboard or touchpad for a while.
This is not so cool.
You should turn on the pbbuttonsd option to rescan devices, then it ought to detect your external mouse/keyboard.
Note that it seems to have a bug in that it sometimes doesn't pick up my internal keyboard even. Oh well.