I was working with an Arduino clone (Osep) controlling an electric pump, when I accidentally fried digital pin 9. It read zero volts no matter what I did. Since I needed to use PWM, I switched to pin 10 and continued on. After I got everything working OK, I noticed the motor would start briefly during program upload, and also whenever I opened the serial monitor. I tried a 10K resistor between pin 10 and ground, but it didn't change anything. I was new enough to the Arduino that I just assumed this was normal behavior.
Eventually I got tired of disconnecting the motor every time I wanted to use the serial monitor, so I started investigating. I found there was .35 volts on pin 10 even when it was set to LOW! Here's the strange part - the motor didn't run all the time (as one would expect) because this model has a brake functon that activates when the voltage is below .4 volts.
Moral: When you burn out a pin, get out your voltmeter and check the other pins! Happy troubleshooting!