I completely agree with aragorn, Simon's document taught me to be a better perl programmer too, knowing what is going on under-the-hood has helped in making some over-the-hood descisions.

And if you are interested in seeing the datastructures Simon describes in real-life. I would recommend exploring the B modules, which Simon touches on at the end of his document. I asked the monostarty about the B modules a little while back, and got some good answers and links here.