I am considering buying an LED display for this project. It would be used to display the value of the PWM signal sent to the H-bridge, as a percentage (i.e. the duty cycle). This would be good because I wouldn't have to use the Serial port on my computer to monitor this value. This 7-segment, 4-character LED display from Sparkfun looks good:
http://www.arunet.co.uk/tkboyd/ec/ec1led4x7ser.htm on how to use it. This particular display can use both NewSoftSerial and SPI, but apparently there is a bug in the SPI implementation: http://bleaklow.com/2010/08/28/sparkfun_are_less_than_electrifying.html.
Over-current protection is still a problem. I need some sort of feedback. Implementing it will cost money. It's not that expensive (Sparkfun sells one: http://www.sparkfun.com/products/9028), but I'm running out of cash to spend. I'll probably have to settle for some auto-delay function when you switch directions, that will automatically slow the motor down before you apply counter-current.