My dear Professor Gupta,
One thing that hasn't been mentioned is that the O2 sensor has to be hot enough for it to work. If you don't notice a _difference_ in the richness after the car gets to normal operating temperature then it's possible that the O2 sensor isn't working. Stand behind your car and take a whiff of the exhaust fumes on startup and once again when warm
j/k. You might want to check out an oil test kit from blackstone labs. Unburnt fuel will foul up your catalytic converter which will cause a buildup of pressure, which will cause ignition, which will destroy the 02 sensor, which will... you get the picture. It's a self destructing loop from then on.
PS: Is this touchy feely enough?