When signing up to wordpress.com or going to the dashboard the SSL connection is not considered secure by recent versions of Opera because the servers apparently do not support TLS renegotiation:
http://my.opera.com/securitygroup/blog/2010/01/23/alpha-testing-tls-renego-fix
http://my.opera.com/securitygroup/blog/2010/06/02/how-secure-is-the-secure-web-ssl-tls-server-stats-part-1
When will wordpress.com upgrade it's servers to a patched version of SSL/TLS?