That felt tip pen scene could do with some work, which should be good for teaching some nice things.
(You might not notice but for one the pens aren't quite on the floor, which makes the shadows look odd.)
Doing a bit of mesh joining should make the models look nicer too.
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http://qoal.kicks-ass.net/ortenga/ub...0x1200_2--.c4d
I set the Stochastic samples and Record density to Low on the second tab of the GI settings, you could make them Medium if you so wish.