I dislike most car rental agencies, with a good reason. National double charged our credit card back in June of 2003, when we were back to the states for a month long vacation. It took most of our vacation to get the situation solved, and it was a good thing that we were visiting family, and not vacationing in the truest sense of the word, or we would have starved and been sleeping in that rental car.
But once again the car rental places have struck. Go here to Carlos' blog Ragamuffin and read what has happened to him. Link to it if you can!