I don't believe Logitech documents this anywhere and I discovered it by accident. At first I didn't think they did anything because it takes a moment or two (close to a second on my machine) for the keystroke to register back at the Mac. The volume keys affect the global sound level with no delay.
Specifics: iTunes 3.0, OS X 10.2, Logitech Control Center 1.02, Cordless Desktop Pro keyboard. I'm now on iTunes 3.0.1 & OS X 10.2.1 with no ill effects - no improvements either. I don't know what the mininum levels for this functionality would be.

