Kevin Smith fell in love with Seth Rogen the day he watched The 40 Year Old Virgin on his DVD. As he writes in his blog:
"...I knew I wanted to work with the guy when I watched him play a video game with Paul Rudd’s character and utter “I’m ripping your head off right now. It’s off and now I’m throwing it at your body. FUCK you!”
The delivery of that “FUCK you!” had me rolling. I rewound that moment multiple times during that viewing".
So, he sent the guy an email, again mentioning how much he loved him in that particular scene, and how much he'd like him to be in his movie.
Seth replied, saying that he'd love to be in that movie - and adding how much he loves Kevin's work, and that he is the reason he started writing movies etc.
This lead to a series of email correspondence (which Kevin fully reveals in his blog), which can be basically described as Kevin and Seth lyrically licking each other's ass.
They also met in Kevin's house.
Meanwhile, Knocked Up was out, followed by Superbad - and Seth became a big star - causing Kevin to fear that Seth will be flooded with many other, possibly better movie-opportunities, or perhaps he'll just won't be able to find the time.
He was right - as Seth had to take a break. Kevin postponed production.
But eventually - the movie was made. And Seth Rogen was, indeed, great in that role.
For the part of Miri - Rosario Dawson, who played in Clerks 2 - was first considered by Kevin - but she was already cast to a different movie.
An exec in the Wienstein production company handed-out a list of alternative actresses for the role of Miri - which eventually lead to the decision of casting Elizabeth Banks, who was also interested to be in that project. She also did a great job in that role.
Zack&Miri is what you get from Kevin, when you let him mix a "straight"
"by-the-book" romantic comedy, like Jersey Girl* - with a witty fouled-mouth dialouges movie like Clerks;
The best of both worlds.
*Jersey Girl was the movie Kevin made before Clerks 2, and the first time he took the courage to stray from his usual formula of "in-your-face-don't give-a-fuck" scripts and characters and tried to make a more "solidic" movie. The movie did not have great success, although, in my humble opinion - it was a really nice movie, and he did a great job writing and directing it. I think the major contribution for it to be not so succesfull - is the sociological and psychological effects from a different movie, released one year earlier, which quickly became known as one of the worst movies ever made, that starred Ben Affleck and Jennifer Lopez, who both also played in Jersey.
Zack&Miri has a simple premise, but with the writing skills of Kevin, it became a really funny movie (audience was literarey laughing their asses out loud at the cinema (Except 3 old ladies, who found themselves at the wrong place in the wrong time, and left at the middle...)) - and at the midst of being loaded with (good) shit-cock-and-pussy jokes - it also manages to be sweet and charming.
Kevin Smith has been doing the same movie over and over again (with the exception of Dogma), but each time he adds new twists and ideas - which causes you to laugh again, like you're seeing it for the first time. He's good at that.
He still couldn't resist giving his old pal, Jason Mewes, a role in the movie. And, as usual, Jay gave a funny performance...
Some fun songs are included in the soundtrack. The song played during Zack&Miri's sex scene (which fitted very nicely into the scene) is one that was not included in the offical release of the movie's soundtrack, and is one that was sought by many, to tell by the large amounts of questions in forums and sites like answers.yahoo.com.
The answer is: Hold Me Up by Live.
And you can also learn about how many was looking for it by reading the comments for the song posted in YouTube.
Another song used in a different important scene in the movie (and fits a little less nicely than the other one), is Hey by The Pixies.
This song also has some history related to Kevin - and to understand what it is, you need to watch the following videos, one after the other: