Solved
You probably have a wiring error.
But that is a terrible tutorial -- you should never power motors from the Arduino 5V output. That can actually damage or destroy the Arduino; at the very least the Arduino will probably malfunction because of electrical noise. Shame on Adafruit.
For a small motor, in many cases you can use a 4XAA battery pack for power, and connect all the grounds.
Are you using exactly the same transistor and resistor value? Please post the code you're using.
Steve
Post a closeup, well focused picture of your setup, showing all the wires clearly.
He's done this at least three times so far ... http://forum.arduino.cc/index.php?topic=542684.msg3699743#msg3699743
Don
Reported to moderators.