Hello all,
I'm working my way through the Arduino Starter Kit. I find myself in the same situation, on project 10, as Pando in this post. I've wired everything up and transcribed the code from the manual, but nothing happens. Zip. 
It turns out Pando's problem was a borked H-bridge. I'm wondering if I'm in the same situation. Here is what I have done to debug the situation so far.
First, I opened a serial connection in the code and printed out the value of all variables before and after all tests and assignment statements (with delay()'s after each Serial.print so I could read it all). This showed me that the switches and the potentiometer were affecting the value of the variables as expected.
Second, I wired gpio pin 9 to an LED instead of pin 1 of the H-bridge. In the above mentioned post, kaning found that he wasn't getting signals from his output pin (he doesn't say why nor how he fixed it). I wanted to test for that. The LED lit up as expected in reponse to switch presses. So I think I can conclude that the signal was also getting as far as the H-bridge.
Similarly, I tested the signal coming from gpio output pins 2 and 3 by connecting them to a couple of LEDs instead of pins 2 and 7 of the H-bridge. Like above, the LEDs responded as expected to the direction switch being closed.
Oh yeah, and before all this, I also wired the motor directly to 9v just to make sure that the motor was working. It is.
Have I covered it? Is there anything else people would recommend I check before assuming that my H-bridge is faulty?
Thanks