Self-checkouts could easily be both faster and friendlier than they are now. If they were treated as express lanes, and took only one form of payment—some sort of loadable store-only debit card, that would also serve as your store loyalty card—then the process would simply become "scan, scan, scan, swipe" (or alternately, "insert, scan, scan, scan, eject iff sufficient funds", in card-lock fashion.)