I've noticed a lot of the negative comments about this title tend to focus on this movie's vulgar, 'stupid' humor. Now let's get one thing straight. Knocked Up is vulgar, absolutely it is, but is is not stupid. Stupid humor is crap like "Mr. Woodcock" and "Good Luck Chuck," movies with no real craft to any of their jokes.
"Jessica Alba fell down!!! Ahahahahahaha!"
"He yelled 'sex' really loud!!! Pssshhahahahahaaheheheheeee!"
Knocked Up, on the other hand, is actually pretty clever most of the time. And even the movie's vulgarity isn't done in an over-the-top, simply-for-gross-out way (cite the fat bitch from Good Luck Chuck). It's what I guess you could call 'relevant vulgarity.' Anyway, the movie is extremely funny. Every joke is naturalistic, but not expected. The movie's characters are all convincing and multi-dimensional, and above all likable. Seth Rogan really does make the movie, though. He is hilarious, but he comes off more like a real nice, frank, down-to-Earth guy. Just the kind of guy you'd like to sit down and have a beer with. The kind of guy you'd more than like to get smashed with. The kind of guy you'd really like to have ill advised unprotected sex with. The kind of guy you'd love to raise a bastard child with. Needless to say, he's the reason the movie works.