Scott, I talked to mechanic at the local GM dealership quite some time back and asked him exactly what the sensor measured. He said it measures idle time, how long the engine is at certain rpms, engine temperature and duration of those temperatures along with throttle position and how long at certain positions. Once these factors all combine and meet a certain programmed limit the computer turns the light on. The oil condition is not tested, oil analysis is much more accurate than the GM oil change sensor and if you're using high grade or synthetic oil is totally useless.
I think thus far these sensors are only on Corvettes and Caddys but could be wrong.