Let's not let Natalie Portman off the hook. That scene with both of them -- the "I'm only beautiful because you love me so much", "No, I'm beautiful because I love *you* so much!" business -- it had me wishing I had a pen with me so I could stab out my eyes and eardrums.
Nice to know I wasn't alone. I was in a theater full of people, so I had to hold my tongue, but every time it was just the two of them on the screen, I wanted to shout "You're killing me!"
I agree Portman is no Meryl Streep, but she didn't have a lot to do in Ep III besides give birth to Luke and Leia. Lucas is no good at romantic dialogue, but it didn't matter that much between Han Solo and Leia, who were anti-romantic (Leia: "I love you!" Solo: "I know.").