<rant>
I cannot fathom not leaving a tip! Most of my stays in places are only for a night or two so I leave one tip at the end... longer term stays I leave it each day. These people work hard everyday cleaning up our messes whether the mess be big or small.
We travel as 2 adults, we don't make much of a mess as we like to keep our stuff in one place not to keep it neat but so there's less chance of us forgetting something. After spending hundreds/thousands dollars what's an additional few bucks a day? Tips don't need to be huge; we usually tip $1 per person per night. If we ask for extra service we'll bump that up.
I can't understand the pettiness of not tipping. I don't say that to be disrespectful or to bash; I simply, personally, can't understand it. Sure if something went badly wrong I can understand not wanting to tip but let's be honest with the 10's of thousand of rooms in WDW and guests staying there what percentage actually have had an issue. I'd say that number is small.
Someone in an earlier posted added up how much more income would be added; it was an extra $6 or something to make their rate be, for example $14 -- it's still hard to pay rent, insurance, buy food etc on that salary.
I don't feel guilty at all giving someone tax free income.

People at WDW do so much to make us smile; how about we return the favour? I don't think it's too much to ask to make someone else's day.
</rant>