I might pay extra for exit row seats, though.
I'd gladly pay $15 extra for an exit row seat or a seat at the front of coach where you get extra legroom (not with a hard bulkhead), as I'm tall.
The problem I have with this business model is that it doesn't improve my odds of getting a coveted exit row seat. So now I have the choice of flying Northwest, and waiting until the last moment and hoping that I can pay $15 for a seat, or I can fly Delta or American (etc) and wait until the last moment hoping that I can get a seat free. I now have an extra incentive to avoid Northwest.
If they let me pay the extra $15 when I make the reservation, then I'd have an incentive to fly Northwest. Unfortunately the airline that used to give me an exit row seat for free every time I booked a flight (at the time of booking, despite being an infrequent flyer) is no longer in business....