My wife uses a Drive med 3 wheel one (Racy looking red beauty ;P) and Northwest has been wonderfull about it. A couple things you may want to consider tho... many of the regional jeta have smallish corgo holds. What I do is to double check our flights and try to get booked on the larger planes (better chance for upgrades anyway). We have had some issues with gate checking through DTW, as they always seem to want to bring the scooter up to the gate for the connection instead of our request to check through to destination. I suppose if we had needed the scooter in DTW and they had assumed we didn't I would be more upset, so they seem to err on the safe side.
We have had some check in agents 'scold' us if the ticket record doesn't show that she is traveling with the scooter, so if you book online, I would suggest calling after your reservation is booked just to let them know you have the scooter.
D