One night, an ambitious and babelicious young journalist (Katherine Heigl) hooks up with a goofball stoner (Seth Rogen), who’s hard not to like but hardly life-mate material. That matters, see, because he gets her pregnant. And she wants the baby. After a sluggish setup, writer-director Judd Apatow (Freaks and Geeks, The 40-Year-Old Virgin) sheds the dumb-joke padding and finds an impressively character-driven stride. The accidental couple’s halting courtship, and particularly their marvelously controlled fight scenes, reveal Apatow as a filmmaker of real maturity and serious ambition. It’s almost like you can feel him getting bored with his own high-concept shtick, and rightly so; Knocked Up really comes alive when it has something to say about the thorny responsibilities — and unexpected blessings — of adult relationships. The whole premise of the thing is a gesture of good faith, which should tip you off to its generous disposition. Also with fine supporting work from Leslie Mann and Paul Rudd as the mom-to-be’s sister and brother-in-law.