I've just added some nice stats to RememberYourFriends.com. It's basically two line charts. One of how many reminders have been sent that week and one of how many reminders have been sent, ever up to a particular week from the very start.
To do this I use the wonderful CharDirector package for Python which is really fast and very easy to implement. These graphs are created on the fly and apart from generating the image it obviously needs to generate the data. Pretty fast I'd say. Will be interesting to see how it will fair when the load starts to get interesting.
Once I get a bit more users I'll start thinking of other funky charts to draw. It's fun.