An idea is proposed by a PHD student of University of Auckland to check
your OO Design on Java. The key point is to use directed graph to
analyze the dependencies between all java classes, and the more
classses involved in some cycle, the worse design it is.
Several Java Open source softwares have been examed in his
research report...
Though it is not the only metric to check your OO design, I'd like to say that it is an interesting thought.