I have to agree with much that has been said in this thread. Tipping is a reward for service. That being said, I tend to reward good service with a decent to good tip (averaging 15%), & will tip more for excellent service.
That being said, however, I will also say that a server can "spend" his tip away too. I'll give an example from tonight when my wife & I went to a local restaurant. We both ordered from the "meal" menu, meaning that soup or salad was included; also, since her came with 2 vegetables to be selected from the list, she had to also make that selection. When she asked about a particular soup, the server said that she could have it, sure, so she ordered it. She also ordered 2 vegetables, specifically mashed potatoes and also fried eggplant.
Now, we get to the server spending his own tip. First, the restaurant did not have the eggplant tonight, so he had to ask whether substituting fried mushrooms would be acceptable. That would NOT be spending his own tip, except that he'd spent the entire time from when he took our order until the time he went in the back chatting with his fellow servers, rather than even checking to find out if our food was ready after approximately 40 minutes at a NOT very busy restaurant; he also hadn't bothered to in any way communicate with the kitchen staff, until he got our meal, and so did not happen to find out that they were out of eggplant until he brought the meals. So, he had to go back to tell them yes on the mushrooms; he went back to tell them, but did not return to the kitchen until we were literally done with 1/2 of the meal that he had delivered. Similarly, I had ordered pasta, but he didn't ask/offer grated cheese, and for that matter, did not return to check (1) if the meals were ok, or (2) did we need anything else [cheese, refill on drinks, anything]. He delivered the fried mushrooms & attempted to just walk away; I had to get his attention to bring him back from chatting to get the cheese & a refill.
Finally, when we were still eating, but, getting TOWARD being finished (but mind you, we both had food in our mouths as well as on our plates), he came back, asked us if we wanted any dessert, & presented us with the bill, all without our having a "choice" but to be rude & speak with food still in our mouths. NOT acceptable in my book (if he'd waited til we were done, or even if he'd just said oh, I'm sorry, I just wanted to ask... & waited a moment for us to swallow before expecting an answer, then he'd have been fine). Finally, when the bill DID get presented, it turned out that the soup ordered by my wife had an additional charge that he had NOT told us about. Had she known about it, she might have not ordered it, but if she had, we wouldn't have been surprised nor displeased by the additional charge. Just tell us things up front, when we're asking you after all, and then it's the customer's choice, not the server's error.
So, did I tip? Yes. I am not ashamed to admit that I left a VERY poor tip to make a point that his service was only worth that number of cents, because it WAS precisely what it was worth. Additionally, I did discuss it with a manager, who asked that I write down what happened, to be given to the owners. I did so, because I wasn't condemning the restaurant for his service, but I was very displeased with the service.
Was this typical for me? No. Do I admit that perhaps he pushed all the wrong buttons at the same time? Yes. Still, I do try to make allowances when the server is being "abused" by the restaurant, having to take care of too many tables & so cannot give the attention that he or she would normally to a table. However, when we're your only client, & you're too busy flapping your gums to take care of your client, then, that will be reflected, too.
That all being said, only once have I had such terrible service at WDW that I have had to "take action" on it; that was at Beaches & Cream when the counter server refused service to us, after having spent 5 minutes trying to make time with two young ladies while making their order, because the restaurant was closed (even though we'd been in the restaurant before the official closing time, & easily seen, had he been looking past the girls). In that case, it wasn't a question of tipping/not tipping, but rather having to talk to the front desk staff at Beach Club for them to pass it along to the dining manager, who was VERY unhappy with the lack of customer service provided by the CM.
Anyway, YMMV, but luckily, most CM's at WDW, regardless of their posting as food service or not, are very good & do earn their reward.
Enjoy the Magic!