I've got a 1 year old 23" display and it's perfect except for a small smudge looking area about 1" tall and 1/2" wide.. looks like someone took a beacon greasy finger and pointed at the screen with it... You really can't see it with the monitor on, but with it off it's very obvious..
I've tried all of the fancy Apple recommended cleaners.. no luck... what on earth could it be?