Tipping... First off, I'd like to clarify something in the original post (reiterating what has already been stated). It is common practice to tip housekeeping services when you travel - not just in Disney. I'm surprised that more people don't know about this.

We tip just about everyone!! We bring about $100 in singles for each trip. Let's see...
Airport parking valet service (Avistar Parking out of NY), baggage check at airport, bartender in airpot (if we stop in), Car Service driver or ME driver, bell services - both at the curb and in the room, all bartenders, waitstaff, golf staff members (when we play), taxi drivers (shuttles to/from golf), and of course, Mousekeeping!!!

One thing that always has gotten me:
Have you ever noticed that people who serve adult drinks outside cannot be tipped, but those serving inside, can be? Get yourself a beer at the R&C Pub and they'll gladly accept your tip. Get the same beer (for a slightly higher price) outside at the kiosk, and they can't take it. Same holds true around the WS and other "outdoor" locations. I always found this an odd policy.