Liv Tyler (Arwen) talks a little bit more about her role in LOTR in this story from CNN. Among the highlights:

"That is nice (having the films done all at once), but there's a part of me that's kind of anxious to get into another role, because 'Lord of the Rings' was so spread out for me. I didn't get that sense of working every day consistently for a period of time. And at the same time, I'm not the main character in those movies." [More]

Thanks to sk0766 for the heads up.