I tip approximately $5 per day, unless it's been a particularly messy day, then I leave a few dollars more. I tip everyday when I'm at WDW. Sometimes, when the Housekeeper does something particularly nice (i.e., noticed we went through all of our coffee packs everyday, so left us extra), I'll find them and give them even more in addition to what we left. I try to bring small bills and fivers to pay for tips for luggage delivery, Mousekeeping, etc. throughout our stay.
While Mousekeeping isn't an officially tipped position, I appreciate anyone who cleans up after me when I'm on vacation, especially someone who cleans the bathroom. Also, I waited tables in college at a comedy club, so it was mostly serving drinks, and it was very hard, very *dirty* work at times (the job included busing and cleaning the room in between shows). I had a ton of customers who didn't tip or didn't tip very well because "she's just serving drinks, it's not like this is a restaurant." So I tend to look at these things from the viewpoint of someone who has been in those shoes. If someone does me a personal service that's hard and often messy, I show them my appreciation through tips.