We've all been there. You're all set to try out the latest and greatest online service but there's a problem - it needs a credit card number before it will let you do anything or even create an account. But you don't always want to give your credit card number to a company that might not still be around in a few months, and it's possible you might even be a little protective of those digits even if it's a well established company because, after all, you can never be too careful.
