An (almost complete) state of the art around the Graph Motif problem by Florian Sikora.
A listing of current (March, 2012) results on the Graph Motif problem, including references to software.
Starts with an intuitive illustration of the problem.
Makes it easy to see why this problem is going to command a lot of attention as more complex (and realistic) modeling becomes commonplace.
Or to put it another way, normalized data is just that, normalized data. That’s why we don’t call it reality.