Revealing mistake: When Toby announces that he's moving to Costa Rica, he gets up and goes to hop the fence. He moves out of frame and when the camera goes back to him, he's been replaced by a stunt double, which can be seen as the double's face is visible after he's scaled the fence. (00:17:15)
Revealing mistake: In the first scene, everyone is in the conference room, just waiting for the block on the TV to hit a corner while Michael is blabbing away. The screen has no reflections, but later when Michael talks to the camera there is a reflection. In the scene you can also see the off shading on the characters in it, making it very apparent that the scene was filmed using a green screen.
Revealing mistake: Michael is on his computer trying to open up PowerPoint in front of everyone in the conference room. He says "what we have to do here is go to run" and he clicks the run icon. However on Windows XP (the version he is using) and all other versions of Windows, clicking "Run" would open a separate window where you would type the name of the program. However, what appears on screen is a context menu as if he had clicked the "All Programs" button. You can even see the highlighted "All programs" button indicating that it was actually pressed. They likely had a PowerPoint presentation running in full screen with screenshots of a Windows desktop on each slide. As Steve clicked arbitrarily on the screen, it would trigger the next slide to appear thus creating the illusion that he was interacting with the operating system. (00:19:16)