On Watchmen Cast Revealed! It's Mostly Crap! at 02/24 1:25pm

Carla Guigino was cast as Sally Jupiter. Malin Akerman is playing Laurie Jupiter, who is not married to Doc Manhattan (though they've been in a long term relationship for awhile as of 1985). Laurie is also younger than the rest of the heroes, so casting a younger actress isn't as out there as Matthew Goode's age. In fact Jennifer Connolly or Rachel Weisz would probably be too old.

Also, Laurie is a very sexual character in the book. Not an "oversexed superbabe", but someone who initiates sex with her male partners, flirts openly, and is definitely considered to be strikingly hot in the world she exists in (she self-references that when she talks about her costume). I don't know about Malin Akerman's acting abilities, but I don't think your reasons for disliking her casting make much sense in the context of the actual story.

Plus, now that we've seen actual footage, and reviews are coming in (from actual comic fans), I think it looks like Snyder did a good job. I agree that the casting was the big question mark in this, but I'll wait until I see it until I decide.