It is so easy to enable Google, Facebook Connect, Twitter, and Hotmail account logins for your site that it makes absolutely no sense to roll your own. Instead of rolling your own features like login, signup, forgot-my-password, confirm-email etc., just implement the above for your sites from the get go. OpenID is good too but I've found almost nobody uses that to log into my sites. 75% are Gmail/Google, 20% Facebook, and rest are Twitter and MSN.