Craig, in the USA, most servers, bartenders, etc. are paid minimum wage and management assumes that they will make most of their income from tips.
I generally tip 15% to 20% across the board to restaurant servers and bartenders. But I have been known to tip considerably more in certain circumstances.
I almost always tip bathroom attendants and carry a stack of brand-new USD $2 bills for that purpose.
I always tip hotel staff -- room cleaners and others -- Generally I tip every every morning -- rates are dependent on a variety of factors -- but generally I leave two $2 bills on the pillow.
Pre-loaded tips are fine on the devices -- Europe has had the hand-held card chargers for more than three decades - it is only now that the US is finally catching up. I generally don't like my card to go off to the back room with the server -- I prefer to do the tipping and paying at the same time.
This is Labor Day in the USA. I also tip the garbage men, postal workers, delivery drivers, etc., generally anyone who makes my life easier on a day-to-day basis. I don't tip these kind of workers every day -- but every so often.
Mark