We tip $1.00 a day for Mousekeeping. My BF used to work in house keeping and she told me that she was easily able to get to 6 or 7 rooms an hour. Even if they are getting the minimun, they're coming out with at least $12.00 an hour if everyone gives them a dollar.
As far as the buffet issue, I don't think you should HAVE to tip 18% on parties of 6 or more. I think 18% is a bit much for filling glasses and removing plates

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I work for the post office and our carriers walk 20 plus miles a day in the heat, snow, rain and cold. No one ever thinks of tipping them.
I tip when it's deserved. If the service is good I have given up to 50%. I have even gone as far as to find out who cleaned our room at POR because she took the time to make towel animals for DD birthday and we wrote her a thank you note and tipped her more.
DH and I disagree on the tipping issue. He worries about our things being stolen if we don't tip enough. I have talked to people that tip more for the same reason. I think it's really sad

that people have gotten to the point where people are tipping based on fear and not if the service deserves a little extra thank you.
We make our own Mousekeeping envelopes. I get Disney stickers and have my daughter decorate them and write a little thank you note on the inside flap

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