From the obsessive compulsive department:
I've been changing my own oil by driving up on a pair of ramps, draining and filling. Based on a slight overfill condition after adding the specified amount of oil and returning the vehicle to level, I know I'm not getting all the old oil out. This makes sense, since the drain plug is towards the front of the oil pan. Oil must be pooling at the back of the pan due to the angle from the ramps. It can't be more than a couple or three ounces.
I'm not worried about the slight excess. Shaving a couple ounces off the amount added next time will put it spot on. I don't like the idea of leaving a measurable amount of dirty oil if I can avoid it, especially on the one vehicle that only gets out of the garage a few months a year.
I suppose I can try and get another pair of ramps under the rear wheels if they'll fit. Jacking up the rear to level the vehicle would work, too, I guess. Any other ideas? Am am I the only nut that worries about a couple ounces of dirty oil?