Same problem with 23.0.1522.60, Win8 x64. I imported a client certificate in the Win8 certificate manager, and I can use the certificate without trouble in IE. With Opera, page keeps loading forever, as mickeyslo pointed. It's not a problem prompting the password (there is no need for asking the password after importing the certificate into the secure store), but managing the secure connection.
I'm a little bit dissapointed with this kind of basic functionalities not working properly after all this time...