Yes, I believe Skar is right about the point my brother was trying to make about Natalie Portman. She wowed both of us in "Cold Mountain", and we both frequently find ourselves defending her to those who have only seen her in "Star Wars." But to the average movie goer, and even more so to the average fan of science fiction and genre films, the first image that comes to mind is Padme Amidala. I mean, how many people on this site read "Natalie Portman" and think "Oh yeah, 2005 Oscar Nominee for 'Closer'"? Personally, it makes me crazy when people refer to the great Liam Neeson as "what's his name who played Qui-Gonn Jinn", but to a lot of people, that's who he is.
Personally, I feel some actors, particularly Ewan McGregor, rose above the material and the CGI better than Portman did. She seems, to me, to be the least sincere of the leads, and her emotions seem too mannered and hollow to me (yes, even by comparison to Hayden Christensen). But when I saw her in "Cold Mountain", I knew that was not due to lack of ability on her part. Sadly, even though I am a lifelong Lucas fan, I must conclude it is largely due to inadequate direction. George is a great many things, but he is no director of actors. Whereas "Cold Mountain" director Anthony Minghella is a lot less exciting and fun, but is superb with actors.
I have not yet seen "V For Vendetta", so I don't have an opinion of her performance there.