Just watched last night's Doctor Who Confidential, and found it impossible to ignore the fact that Billie Piper wasn't even in shot when the cast did their read-through of the script.
Mind you, this is the same person who, when asked "Were you a big sci-fi fan before [_Dr Who_]?" replied "Not really. But when I read the scripts, I found it was a great balance between sci-fi, which can be a bit detached, and real, genuine, emotions." (Thanks to
Ansible for that gem.)