Thanks Rx400h. I had already read that thread, but didn't really find anything useful for my purpose.
As far as your question, "Is there anything on that seat when the light is illuminated?", the answer is yes, that would be me most of the time, and I weigh in around 250, so I don't think that too light a weight factor is the issue.
Also, as stated before, while my wife and I are driving down the road and I unbuckle the passenger seat belt, neither the seat belt light nor the beeper comes on to alert us of the condition. I know that the air bag and seat belt work together in the system but I'm unsure of which is the cause and which is the result.
Sure wish this had happened a few months ago while still in warranty...arggg. :(