Thank you all for your responses. This is very useful information. I am new to Arduino it is not clear to me how big the market is for shields. What little I could find regarding Arduino sales seems quite impressive. My intention was to address the elegence of system integration using shields as apposed to functions wired into the host. I was hoping there would be intrest in not only motor drivers but optical detectors, laser drivers, and analog sensor interface shields offering high performance and robust but user friendly software. Many of which could be realized for a reasonable price. The key is the desire to simply plug the function directly on the Arduino and run.
T. Boyd