Visible crew/equipment: When Shawn and Gus gets out of the car at the Mausoleum Parking, you can see the camera man reflected in the mirror inside the car.
Continuity mistake: In one of the first shots showing Agatha's friend Lucy behind the police line, Gus is visible in the background talking before Sean and Gus arrive at the scene.
Factual error: In the flashback at the beginning of the episode, Shawn is wearing a Knight Rider T-shirt. This flashback takes place in the 80's, but the art printed on the T-shirt is a picture-perfect copy of the cover art from the US DVD release of Knight Rider Season 3 - this DVD set (and the cover art style/arrangement) was not released until 2006: http://en.wikipedia.org/wiki/Knight_Rider_%28season_3%29.
Continuity mistake: When Shawn flashes back to remember where he has seen Pierre Desperaux, he flashes on a photo of Pierre in Lassie's apartment next to Ernesto Chavez (on the right) on Lassie's wall. Going back to Season 3, Episode 11, when in Lassie's apartment, there is no photo next to Ernesto's photo.
Continuity mistake: Just before Gus is awoken by noises in his apartment, there is a shot of his alarm clock. The time shows 6:07PM. When he gets out of bed, the clock says 7:01 (cannot determine if it is AM or PM). Even assuming he just lay in bed for an extra hour, he then tracks down Lassie who is about to eat lunch.
Continuity mistake: When the bank robber enters the mausoleum, his hands are empty. When Raylene points her gun at everyone, he raises empty hands. After Lassie and Juliet arrest David and Raylene, the bank robber is holding a slushie cup.
Continuity mistake: When Shawn and Gus are driving the boat at night, we see the coordinates on the GPS tracker - two seconds later (real time, as they are talking), the coordinates have changed; now they are about 37 miles from where they were, so they must have hit 65,000 mph for those 2 seconds. In case my math needs correcting, the first set is 34 06' 50.25" N x 120 17' 41.31" W and the second set is 33 57' 40.21" N x 119 35' 56.58" W.
Continuity mistake: When Shawn calls the first student up to the board to write a number, firstly the written number is 6.00214, which is an incorrect Avagadro's number, but it is not always this incorrect number. At some point during filming somebody changed it to the correct number: 6.02214, and you can see the number actually changing back and forth between the two numerous times during this scene.
Continuity mistake: A man attacks the judge by running out of the shower. When he runs through the shower, a shower curtain is draped over him. For most of the scene it is over his head, but when he is dragging the judge into the shower, the curtain has moved off of his head and is even gone completely in one shot, perhaps to make the actor more visible.
Character mistake: When Shawn is checking Ed's book of valuables, the crown that Shawn thinks Despereaux will steal, has a listed value of "950,000 - 1,000,00,000 USD." I guess it's really, really(!) valuable, enough that a whole new numbering system was made up for it.
Continuity mistake: When Shawn sees the box with the dead doctor's files, Regina Kane's file is visible halfway back in the box. He then tells Gus, "All we have to do is find Regina's." (Which he was looking straight at, but let's call that a character mistake.) A few moments later, we cut back to Shawn and Gus and Shawn finds her file in the front of the box.