I was looking for the same thing. Every time the reed switch is closed you want to know that the motor went a revolution http://arduino.cc/en/Tutorial/ButtonStateChange
shows this functionality.
"The sketch below continually reads the button's state. It then compares the button's state to its state the last time through the main loop. If the current button state is different from the last button state and the current button state is high, then the button changed from off to on. The sketch then increments a button push counter."
I want to use this to operate a linear actuator for a satellite dish position. I would like to be able to store the number of button pushes and change the position up or down by comparing the current position to the desired position.
In this way I want to track the sun for a parabolic solar hot water heater.