IMac :: 2009 - Brightness Settings Won't Save?

the monitor's default brightness setting is far too bright for my eyes, so the first thing I did was to open the System Preferences pane and reduce the brightness setting. That worked fine until I shut the computer down. On rebooting, the brightness returned to its default highest setting. On my older iMac G5, the brightness setting always stayed put. It isn't a huge problem since adjusting the brightness setting does work, but I don't want to have to adjust it every time I reboot my computer.

I spent two hours yesterday on the phone with Apple support trying to fix the problem, even going so far as to reinstall the system software with no success. The woman on the phone finally suggested that I return the Mac for a replacement.

Has anyone else here with a 2009 iMac experienced this problem? Is it possible that it's hardware related? If so, could this be the tip of the iceberg suggesting a potentially larger problem down the road? I would have guessed it might be a software glitch. (The new iMac has thrust me, finally, into Leopard; until last week I was using Tiger on my older G5.) I bought the 3-year Apple Care with it--since the new iMacs have only been out a week, should I wait until the next Leopard update and see if that fixes the problem?