I found when watching Coraline that my eyes adjust after awhile, and the 3D effect doesn't look as good by the end of the movie as it did at the beginning. This could really be a problem for a 3-hr-plus movie like Titanic.
I have to cast another unimpressed vote on the current RealD 3D process. From several stories I have read, it seems that many believe this latest 3-D technology works very well. When I watched Coraline 3D, I didn't feel strain on my eyes, I just wasn't impressed with the image quality. The image felt limited to me. I have worn normal glasses to movies, so I don't think it is just because of wearing glasses. The image feels dimmer, and boxed in, as if I weren't watching a big screen.