This may not be relevant to most users now since my display is so old. I have a 20" Cinema Display - the plastic bezel type - purchased around 2003. Still using it as my only display. I lost use of the brightness and usb hub probably 6 or 7 years ago. It just stopped working one day and I tried different usb plugs on my mac pro, rebooting, etc. I thought it may have been related to an OSX update, but eventually wrote it off as a monitor hardware failure. I've been leaving the monitor usb cable unplugged ever since.
Since upgrading to OSX Lion I decided on a whim to try the monitor usb cable again. While the system was running I plugged the usb cable to the back of the computer and immediately heard some hard drive activity, as it was responding to the device. I tried the brightness controls on my keyboard and it worked again! The controls on the monitor bezel work also, and the monitor usb hub.
Maybe it was an OS issue that was fixed in Lion? In any case I'm glad to have it back.
10 year old monitor still good as new. I have picked up a slight backlight hum if not on full brightness, but I guess that is common.