Is It Worth Getting a Warranty for a Used Car at a Dealership?

After you buy a warranty for a used car at a dealership and something is wrong with the car and you bring it back to them, I heard that dealerships will usually tell you that there’s nothing wrong with the car and refuse to fix it. Is this true or do they usually fix it for you without giving you a hard time? Is it actually worth buying a warranty?

Suggestion:

No, I made that mistake once and not again.
The car developed a problem in less then 90 days, so the warranty was not valid because it was preexisting. That was what the warranty said, I had to pay for the repairs and the warranty was not needed for any repairs that equaled the cost of the policy.
Now if I was buying a Toyota, Chrysler, or GM product I would think twice because more then likely they will break down. But I drive Fords, Mazda and Honda products and in ten years I don't think I have spent 2000 dollars on any one of them. I use the figure 2000 dollars because the last time some one tried to sell me an extended warranty that was the figure quoted for only three years worth of coverage.