Regarding the use of a credit card... I do not think you have much to worry about. United States law provides that you are only liable for the first $50 of unauthorized use on a card and many credit card companies even waive this first $50. So if there was an unauthorized charge on your card, there is no real risk of a significant loss.

An update: I'm attending CLIC in April (when I could get a good plane fare) and I used CLIC's website to enroll. Everything has worked out using the web site--I got an e-mail confirmation a few days later.

I'm looking forward to going!