Also well said. And it's worse than that - when you allow your users to log in with OpenID, you don't just give up the marketing value of their email - you give

Also well said. And it's worse than that - when you allow your users to log in with OpenID, you don't just give up the marketing value of their email - you give it away to a random third party somewhere on the Internet! Your customer's OpenID provider gets to know her email, her personal information, the sites she visits, the exact times and dates of every login to those sites, even her passwords. The provider also gets to show the user a page at a critical time - the time just before the user signs on to a new site. (Or is it every time the user logs in? God, what a bonanza that would be.) This is the kind of information and access that Google has turned into billions of dollars - only it's potentially more detailed, and more complete. It sounds like a DoubleClick executive's dream come true. No wonder that every big Web company is falling over itself to become an OpenID provider, even though very few sites actually support OpenID logins. What's the average business willing to pay for an ad on its competitors' actual login pages? We may soon find out. So, yeah - without even getting into the potential security issues, the very real user-confusion issues, and the terrifying ten-percent-of-my-users-can't-login-because-of-a-bug-on-someone-else's-site, now-wtf-do-I-do? issues, I'm not sure how many sites outside the Geekosphere are ever going to support OpenID.