As a restaurant manager I can offer some amazing insight into this topic.
Yes there are spiteful servers out there, it's a given. But they are not everywhere, and usually you can tell right away what your server is thinking. Of course they are actors, they were trained to leave their personal problems outside of work. They have to because if they let those problems show they will not make any money. One thing ALL customers should remember is this..most servers are only being paid between $2.00 and $3.00 an hour. So if you don't leave them a tip, their children might not eat this week or their car might be repossessed. Could you imagine doing your job for $3.00 an hour? I couldn't. Now imagine that your job consists of dealing with people who come in expecting you to wait on them hand and foot. Still don't like it do you? Everyone has a bad day, but remember the most important thing when dealing with your server. Yes they have the ability to make your entire meal miserable, but they are not the one cooking the food. So if your steak isn't done, don't yell at the server. If your eggs are overcooked, your server didn't do it. If the kitchen put onions in your salad, it was not the server! By not getting angry and over reacting you will be saving yourself a lot of hassle. Most servers will be happy to have the kitchen make you a new item, especially if you ask nicely, are polite, and realize it is not always their fault.
Another item to remember especially if you are a regular customer is that your servers have EXCELLENT memories. If you were rude, obnoxious, demanding and didn't leave a tip the last time you were in odds are, your service will not get better. Servers talk amongst themselves, just because it is not the same person the odds are that they already know you won't leave them a tip. At $3.00 an hour with no tip, I wouldn't want to wait on you either. However, if you left a decent tip last time in spite of having some difficulties your server will remember how nice you were about it and go out of their way to make sure everything is perfect this time.