Monthly graphs would be somewhat helpful. For example, you could decipher that the AC uses a lot of power if the graph spikes in summer.
Daily graphs would be way more helpful. For example, you can see how much you saved on a day where you were out and used no power.
Hourly graphs would be still more helpful. If you knew you watched TV from 8-9, you could see the cost of an hour of TV.
Real time graphs are the ultimate. Not only do you get all the benefits of the above graphs, but you can go around your house flipping switches and see exactly how much each appliance costs to run. You can spend an hour messing around and reduce your power bill significantly--a savings which you'll realize every month.