Windows XP and Windows Vista save username and password information for network resources and services like Windows Live on the hard drive of the operating system. If you want to check if and which usernames and passwords are stored with the option to remove some or all of them you can do the following.
Avoid multiple login names with OpenID
I really like the idea of an open and decentralized standard which allows you to sign in to
multiple websites without entering your username and password over and over again on every site that requires you to login to
vote (digg.com), comment, or participate in other means. There are so many sites where you have to login to use basically the same features that you used on another site just before you visited the new one.