Reminds me of Firmata project [0] Does pin control, but also PWM, analog, and extensions. Uses existing well documented protocol, has firmware for every Arduino and other boards, GUI tools and bindings for a lot of languages.

[0]http://firmata.org/wiki/Main_Page

Thanks, that might be useful. I figure all of my projects have been done before and better in some way. Most of the fun is in writing the code.

This seems like a somewhat similar idea to the USB Bit Whacker -- UBW <http://www.schmalzhaus.com/UBW/index.html>. The original UBW used a PIC 18F2550 directly connected to USB.