I've only sailed NCL and VV, so I can't speak to other lines. In my mind, that whole "no upselling" thing cannot be stressed enough. It's so nice to go to a show and not spend the first 15-20 minutes listening to the CD selling raffle tickets. How refreshing it is to not have to dodge photographers during dinner.
On Valiant Lady, my partner had a question for sailor services, and I just kinda' wondered around the area waiting for him. A rep from "Get Lost" (MVNN) asked me if I needed anything, and I asked him a random question that popped in my head. (I think it was about how full our sailing was.) He actually answered my question without trying to sell me anything!
That, in turn, made this the first time I've ever bought a future cruise credit.