There has been quite a lot of discussion of OpenID in the rails community over the past few months. I’ve found it very straightforward to implement and very helpful, though the number of users who have OpenIDs is still small and so depending on your users you will still either need to provide a standard username/password or make it very easy for people to create an OpenID.
A few links:
I wrote about it in February: http://jystewart.net/process/2007/02/openid-for-a-rails-app/
Dan Webb wrote a good tutorial: http://www.danwebb.net/2007/2/27/the-no-shit-guide-to-supporting-openid-in-your-applications
There’s a plugin in the official repository: http://svn.rubyonrails.org/rails/plugins/open_id_authentication/
Eastmedia have a plugin that brings together restful_authentication and open_id_authentication: http://identity.eastmedia.com/identity/show/Restful%20OpenID%20Authentication