Twitter, Facebook, or even GitHub authentication is certainly de rigeur, but I must admit I thought OpenID had fallen off the radar and I haven't seen any interesting new projects supporting it lately. Even 37signals gave up on it mostly due to lack of use: http://productblog.37signals.com/products/2011/01/well-be-re...

Nothing against OpenID, per se, but it doesn't feel like it has taken off. Or maybe the big sites that are using it are just getting on with it AOK :-)