Yes - we started having intermittent issues starting this past Friday, then complete failure today. From Y! developer forums, it seems others are having the same problem - http://developer.yahoo.com/forum/OpenID-General-Discussion/OpenID-login-with-Yahoo-broke-today/1386713784256-49fd81b6-7752-4c9f-8b7c-728235c46bae
And in general testing a number of OpenID sites, Yahoo login doesn't work