I tip for all 3 categories listed.

For room service, I will usually add a small tip on top of the service charge. Personally, I just think it is a little more effort to take food from the kitchen, to the elevator, up to my floor, then to my room, then deal with me not having a placed cleared off for the food, etc., than the effort involved from a server in a typical restaurant. So I try to make the total tip more like 25 or 30% instead of my standard 20% restaurant tip.

To the other poster, I haven't noticed a "tray charge" but I'd probably just assume that they were charging you for the room service tray and you were free to keep it, just like with those cool little bottles of ketchup, and jars of jam, etc.

And to the same poster, I have never had a waiter openly complain about a tip or lack thereof, but if it ever happens I will make sure that I stand in the middle of the restaurant and loudly tell them exactly what was lacking in the service delivery to warrant their tip amount. Preferably get the manager involved as well. I put a lot of thought into my choice of tip amount and it ranges greatly, from 0% to 50% solely dependent on service level.