People need to stop whining about them casting too young. Seriously, do you think they're going to not use make-up or something? There's no way they would leave her in her mid 30's playing the mother of Laurie. She'll look like an old woman when needed.
The same goes for the current day heroes. Just because they cast a 20 or 30year old actor doesn't mean they're staying that way. Look at Rorschach, he's the only character who's face isn't shown in flashbacks, and they cast the right age. Everyone else, save Crudup as Manhattan, will be aged up and down for the appopriate scenes.
That said, this is so far the only casting choice i've really gotten excited over, but that's because this is the only one I really recognize. I'd seen Crudup in a few things, but other than that I've never seen any of them. Carla Gugino is a freakin' babe though, so I cant wait.