The Examples are great to get started. Good job!
I found some mistakes though, and would like to post them here:
In this tutorial:http://arduino.cc/en/Tutorial/Tone2
1. The text says "Connect one terminal of your speaker to digital pin 9", the example code also writes to pin 9.
But the comment in the code says "8-ohm speaker on digital pin 8" and the example-code in the arduino-SDK also uses pin 8. This could confuse beginners.
2. In this picture: http://arduino.cc/en/uploads/Tutorial/arduino_speaker_photocell_bb.png
The black wire on the left top side is unnecessary.