Does the oil life monitor in my 01 SSEi work strictly on mileage, or does it consider additional operating conditions?

from gm.com,
The system itself uses an algorithm that tracks engine revolutions and temperature and predicts oil life based on these parameters and driver use.

i think its bogus, mine always goes way over. i just change it every 5k. i do mostly highway.

Based on that, the oil life monitor will show the need for an oil change at the same interval for synthetic oil as it would for mineral oil, since it is monitoring the operating conditions, not monitoring the oil condition.

Is that the case?

yep, it also says the monitor is calibrated for the oil called out in the owners man.