I'm sorry that you feel that way. I definitely understand the feeling of being burned, but I've never had issues with something like this, as a user myself of services with a free trial that requires a credit card.
Things like Twitter and Hacker News, where you can broadcast your displeasure of a company's terrible tactics would make it difficult for a company to keep signing up new users if people are complaining about it. The only companies that I see getting away with stuff like this are huge companies who don't care about their customers anyway, like Tivo.
All of my apps have a prominent link in the user settings panel that lets a user cancel their account/billing with one click.