OpenID Explained: "Regardless of whether you use OpenID or not, you should be careful about your username and password. When you type your username and password, make sure you're actually on the website you think you are (i.e., check the address).
Aren't I entrusting my whole identity to one website?
Yes and no. You can, if you like, have multiple OpenIDs, each of which has some information about you. (In fact, many websites let you associate multiple OpenIDs with the same account.) But, that ruins the simplicity of only having one username and password. That's why it's smart to get your OpenID from a website you trust, and one that you expect to stick around. See How do I get an OpenID? for more information on choosing a good OpenID provider."