Is there some sample code for operating a servo with an Adafruit Motor Shield?
On the Motor shield the servo headers are directly connected to pins 9 and 10 (I think 9 is servo 2 and 10 is servo 1).  So you can use the standard servo examples using pins 9 and 10.  

If you need to power the servos with an external power supply you must cut a trace on the back of the board -- the silk screen tells you where to cut.  Then you need to connect power to the "Opt Servo" input.

The power to the servos is not changed by the power jumper used for the DC/stepper motors.