I saw Baby Mama for the first time over the Thanksgiving holiday; it was okay. There were some funny bits, particularly Steve Martin's "New Age guru by way of Steve Jobs" schtick, but the plot suffers from the same thing that has infected Judd Apatow's comedies and their imitators: We are given no reason why someone as educated and cultured as Tina Fey's character would ever associate with, much less choose to have a baby by, someone as completely the opposite as Amy Poehler's character. Much as Katherine Heigl and Seth Rogen were paired off sort of inexplicably in Knocked Up, two people of opposite characters are thrown together, even though at least one of them can, and ought to, walk away. Yes, Baby Mama is a conventional buddy comedy, and you need something to get the laughs going, but it's still kind of hard to ignore, isn't it? If you're going to have smart people do stupid things, there should at least be some kind of story behind it.
Of course, this problem is an old one in comedy. Why, for example, does Alceste in The Misanthrope fall for Célimène? Is it because he really doesn't believe in his ideals? Is his hatred for society just a front? Is it just irrational? Alceste isn't a hypocrite, the way, say, Tartuffe is -- or is he? He at least struggles with his ideals, rather than cynically peddling them for personal gain. In any case, I think there's a lot of comedy to be had in exploring why people make choices they know full well aren't in their interests, but I haven't seen anything lately that goes in that direction.