I have to respond to the posters who don't want to put their credit card information online. Every time you hand to a clerk or waiter, they have the chance to use the information, sell to someone else or just give it away. Someone who is intent can take the information from your mail or garbage. And the information is already online - every credit card company in the world store their records in electronic files.
If you use only sites that are secure and encripted, you are about as safe as you can be.