The following statement always sounds crazy to anybody who does not work in the movie business: making a movie is boring 90% of the time.
Just like any job, it has its ups and downs. I've found the per-hour formula to be about 40 minutes of nada, 5 minutes of prep for actual work and 15 minutes of working. It works the same no matter who you are on set - the gaffer only works 10 minutes per hour, the costumer works 10, the camera loader, the script supervisor, the hair and make-up team - everybody on set works part of an hour, filling the time until a movie gets made. But everybody needs something else to do for a good chunk of any given day. That's why actors want huge trailers and exotic shooting locales - to stave off the unavoidable boredom.
Despite the exciting title, "Zack & Miri Make A Porno" is mostly "Zack & Miri Hang Around Set Debating the Hit Series LOST." We are obsessed with this ABC show - is Ben ultimately good or evil? Can Desmond time-travel? Should Kate be with Jack or Sawyer? On this point, I argue the show is doing it perfectly. Kate gets to have her cake and eat it too. Both guys love her, she could have either one if she put her mind to it or both at once probably. To choose would not only kill the debate but also the excitement and mystery. That Michael was Ben's "Man on the Boat" was a constant source of debate, although also the worst-kept secret of the show so far. I could go on. On set, I do. On and on. Until Kevin makes us shut it because the last episode is still unwatched on his TIVO.
Another time-killer might be "Zack & Miri Re-cast Old Movies With New Actors." Or "Zack & Miri Debate the Best SNL Skits of All-time." Or "Zack & Miri Take A Nap." You get the idea. So if you ever visit a set, bring your pop-culture A-game (and maybe Boggle). You will die of boredom without them.