You see a fair bit (in the Geek community anyway) about OpenID. It seems like a good idea. I\'m developing a website that will be targeted at a somewhat less geeky audienc
It is good as an addition to normal registration, but is not very easy to use if it is the only way to log into your site. Look at registration on stackoverflow - all sites are specially mentioned to help people understand what is this all about. And this site is for geeks :) So the minus is complexity.
Also see this link