CommanderBond.net quotes an interview with Eva Green, who played Vesper (brilliantly) in Casino Royale:

Green also mentioned she was happy not to appear nude in Casino Royale, saying: ‘I’ve been nude in a film before (The Dreamers) and found it very troubling, so I was quite glad not to be in this film. In [Casino Royale] shower scene—you remember?—they wanted me to strip down to my panties. We had a good fight about that. I used to go to Daniel and ask for his support.’

I think this is so interesting because it is one of the most affecting moments of the film, and to me, part of what made it work was that she was fully clothed. The fact that she went into the shower fully clothed, well that said so much about her mental state, whereas if she’d been nude it would have had less of an impact. Think about it; you go into the shower and then become upset and cry, well, that’s happened to lots of people. But you’re so upset you can’t even get it together to remove your evening gown? That’s a whole ‘nother level.

Of course, having seen The Dreamers, it wouldn’t have occured to me that Eva Green might have refused a nude scene. But how interesting that a scene they wanted to do nude turned out better because she drew that line.