Well onstage, she's playing a role...I don't think there's any requirement that says someone has to be as personable offstage as the roles they play on. The several times I've met her, she's been nothing but sweet. She's also, in my opinion one of the most gifted actors of her generation. She's wonderful in DRS, but she was simply amazing in The Normal Heart last year at the Public.
I think assuming someone needs to be a certain way because of their career or G-d forbid, who they're married to, is a touch absurd. And as I said, I'm sorry for other people's experiences but I've never known her to be anything but extremely pleasant.
"There is nothing scary about life, if you are not attached to the results." - Conversations With God