On paying for twin seats - on my regular route I prefer to sit in one of the last three rows of the 777 (twin seats) as economy deplanes from the back door onto a bus. Since the introduction of paid seating for Gold members, I've learnt that there are always several pairs of twin seats available at check-in, on this South Asian route at least - few others want to pay, either - so I just change my seat to a twin an no cost during on-line checkin. Not sure that would work upstairs on a high-Y A380.