The funny thing isn't the actual movie Zack and Miri Make a Porno. It's the fact that Kevin Smith is now making the kind of movies he mocks. If anyone else had made this film, Smith would be on a college campus right now ripping it to shreds.

It's a bad romantic comedy with a core friendship that you don't believe at all (and a budding romance that is laughably thin). It plays like a spoof of romantic comedies but if that's what he was going for, it was too close. When you hear a song from Live playing over a slow-motion "Aha, I realize how I really feel about you." moment, you think it's a spoof but then there's no punchline. 

Also, they get next to nothing out of the premise. If you think about making a movie about random people making a porno, there are tons of jokes that you could think of. Zack and Miri doesn't really get much out of it at all. Only a few "Making of" jokes; the rest of the laughs are the typical Smith dialogue. There are some funny lines but not enough to make the film worthwhile (and you'd like to think Smith has developed a little bit over the years). 

Craig Robinson is hands down the best thing about the movie and really needs to get a leading role in something but even he can't make this film worthwhile. Unless you are a die hard Kevin Smith fan, I'd skip this one.