Here is a little more detail on when and who to tip:
Valet Parking:
I don't recommend this, simply since you can easily park your own car. But if you do, tip $2-$5 each time you request your vehicle.
Bell Service:
When you check-in you can either pull into the car port at the front of the hotel or go to temporary parking. When you pull into the car port, a bell will greet you and ask if you'll want help with your bags. You may have two different bells help you - one to the front desk (or temp. storage area) and another to bring your bags to your room. I always tip both times - when given a claim ticket at temp. storage -AND- when a bell brings the bags up to the room. The rule of thumb is $1 per bag or other item (ice chest etc.) Remember, you can opt to handle your own bags, in this case you don't tip anyone. You can check-in, then go park your car yourself in guest parking.
Housekeeping:
This is an old tradition that is rarely still followed. I generally don't tip housekeeping, but if you have the extra money and the service is good - leave an envelope CLEARLY marked "Housekeeping". Any amount would be appreciated and it is a very nice gesture, especially if you leave the room a mess like some people I know
Room Service:
Tip similar to how you would in a restaurant, but obviously do so when your food is brought to your room - not after. Double check that gratuity is not automatically added to your bill (I can't recall seeing this at the GCH, but certainly double check) - either way, still tip something for the delivery to your room.
Misc:
Whenever you request anything that is brought to your room by a person and you answer the door - coffee pot, roll away, sheets, towels, etc - you tip this person. A couple of bucks is fine.
Once additional thing that I highly recommend is that you contact the hotel manager should you encounter an outstanding cast member in the hotel (a little note left at the front desk will suffice.) Nothing beats good service and attitude and sometimes it's hit or miss at
Disneyland Resort. If we all reward outstanding service, I feel it creates motivation and perhaps a demand for it. Do the same if you encounter poor service, but be polite and specific without emotional language.
I think that pretty much covers it!