I appreciate all the input. Yes, I have shifted to 2nd while slowing, and then after starting out (when the RPMs got high) said "OOPS, I forgot AGAIN!" and bumped it back to Drive. And I have noticed how smart the computer is (after light braking for several seconds on a downhill, it will disengage the overdrive by itself, with no input from me via the shifter or O/D button). So, unless descending a long downhill grade, I'll forgo any moves to lower gears, and let the computer decide.
What about SHIFTING TO NEUTRAL while approaching a stop light that is red? It bugs me that long, gradual stops (like freeway offramps) that would be effortless in a "shifter car" require much more braking with an automatic transmission (especially as the speed gets lower). Shouldn't I shift to neutral approaching a dead stop from 40 mph, use the brakes to stop the car, and then (when it's green, either stopped or slowly moving forward) bump the shifter back into Drive?
Again, input is welcome. Will shifting from Drive to Neutral at about 40 mph, stopping, and then (while at a stop), shifting to Drive also cause more wear and tear ('cmon, it's all computer controlled, right?) than just leaving it alone?
As has been pointed out, brake pads are cheap compared to engines and transmissions. I want to do whatever makes the most sense in terms of maintenance costs for the long term, and good gas mileage. Thanks for all the input!