FYI: if you turn the screen brightness all the way down, the button backlights turn off. I'm not sure if this is only true with the Custom ROM that I have (DCD 3.0.4 running Windows Mobile 6.1) or if it occurs with the stock ROM running Windows Mobile 6.
Want an easy way to adjust the backlight from the Today Screen? Try Metrix 2.1.1
It's a FREE today screen plug-in.