A couple of weeks back I tried to login to signon.com, my preferred OpenID provider. I use signon.com because it accepts Information Cards for authentication, so that's one less password to remember. However it didn't work; which was strange. I noticed that blogs I had used Information Cards on before told me they couldn't recognise my card either.
It appears that someone listened to the problems with SSL and PPIDs I blogged about in February and this has broken the login. The change isn't a bad thing, it removes the dependence on the SSL chain so when you renew your certificate your users will still be able to login, however the lack of warning and no notification of a breaking change in the 3.5 readme is pretty shoddy.
Mike Jones blogged about it a few days ago; but the breaking update has been out for a couple of weeks now so, if anyone was using it in anger, identity providers have had two weeks to ponder what the heck went on and why their users had to register their cards.