Seriously, what has Portman been good in? Awful in Star Wars, Other Boleyn, Hesher, Closer (Still shocked she was nominated, I thought Roberts acted her off the screen) SO BAD in Brothers. I can't think of anything besides MAYBE Black Swan. She is an awful, wooden actress who happens to be gorgeous. Which, to be honest, IS half the battle.
At least Diaz was excellent in a few films (Something about Mary, Being John Malkovich, Vanilla Sky)
Bullock I don't think is an awful actress, but I just am not really into the rom-com genre, and she seems to have lived there for the past decade.