Unless it gets hacked. Then it's all of sudden not so much fun anymore. >_<
My steam got hacked once, but because I buy all my games from retail stores they couldn't get any creditcard information or anything else sensitive.
Credit card information is stored locally. If someone logs in to your account from another computer, they do not have access to your info.
Valve confirmed it themselves... and the article is all over the web.
Though, like I said, it never happened to me so maybe you're right.
[Edited by Monkey007, 11/29/2011 3:23:48 PM]