To me the maid is the most important person of the staff. It does NOT bother me that Marriott is leaving envelopes in the rooms.
I have ALWAYS tipped the maid at the hotel on a daily basis because you don't always have the same maid everyday. I leave a note that says "Thank you for cleaning the room" with a smiley face on it, money, and a chocolate bar.
It is AMAZING the service we get from housekeeping, and often our room looks like a linen closet they leave so many towels, toilet paper, etc. Many a maid has left me a thank you note in return. In the Middle East along with leaving tons of towels they also strip our beds everyday, make lovely towel animals and even put rose petals on the bed. Apparently they are enjoying the money and chocolate I leave them as much as I enjoy the fantastic service I am getting. I really appreciate CLEAN rooms and good service. Some of the thank you notes that the maids have left have REALLY touched my heart. It also makes me happy that I have made someone elses day easier because having a clean well stocked room makes me happy.
I remember checking out of a hotel in Istanbul and the maid was blowing me kisses as I left. I have been hugged by so many maids, and told many times "God bless you" as I was leaving to check out after a week or 2 stay. It is amazing how appreciated you can be from strangers, and some family members don't even acknowlege a gift.