I always tip tipped positions, even when the service is pretty rotten. I've worked those jobs (server/hospitality management/event planner, and WDW servers are NOT representative of the industry) and feel for them. Rotten service tips will be minimal (10%) and something is usually said about the rotten service. Non-tipped positions, it really depends on the service I receive.
Our last trip, Boardwalk Inn, to WDW, the mousekeeping was horrible. I always leave a clean room; I just can't live in a mess, especially with 5 people in a small room. To give you an idea of what I was talking about, mousekeeping didn't even clean on some days. They were also always taking towels away, despite requesting *more* towels; 3 bath towels, 1 hand towel and 2 washcloths for 5 people just doesn't work. BTW--the hotels do not change your sheets daily unless you request it; they're changed after a guest checks out and at the one week mark;
DVC actually gets better service there. We just had major problems with mousekeeping; we did not tip even though I had planned on it.
I do not believe in rewarding a job that is not only being done badly, but not being done at all on some days, when not a tipped position. Now, if the service is good, and especially above and beyond, I will certainly tip. It is my opinion that is what tips are for. On a previous trip to AKL, my DS (then 3) had his one and only bedwetting accident; yeah, I tipped--big.
Keep in mind that tipping is fairly regional too. It is much more common to tip everyone in the east and to tip very few positions in the south. In the south, you do not tip delivery people, except food; they'll look at you like you have three heads. Of course, in the south you can live better on less. A lot better on a lot less.
As far as rotten work--well the garbage people take the cake on that. I couldn't live without them, and they make crap. They work hard for very little money doing something most people wouldn't do for a lot more money. You could offer me a 7 figure salary and I still wouldn't do that job. For those who tip blindly, do you tip them? And I mean regularly, not just at Christmas.