Continuity mistake: In the scene where Shawn is brought into his childhood bedroom to investigate Allison's abduction, there is a "Peeping Tom" band poster visible behind him for a few seconds. This was Shawn's bedroom in the 90's, and "Peeping Tom" didn't exist until 2006.
Ferry Tale - S5-E7
Plot hole: The cops storm the ferry and recapture the 4 prisoners, only to quickly discover that two convicts swapped places with passengers and escaped on a medical boat. This boat powers off and we're later told "by the time we caught up with the boat they'd made their escape", but there's just no way that's possible. They had barely a minute's head start, in wide open water, with multiple high speed police boats in range/sight of them the whole time.
Ferry Tale - S5-E7
Continuity mistake: When Young Shawn tapes his and Gus' legs together he puts the tape on the ground. When they start to run it has disappeared.
Chosen answer: "Psych: The Musical" was supposed to air during the regular season 7 schedule, before Chief Vick is suspended and Jules discovers Shawn's lie, but the network decided to push it back to air as a special episode, sort of as a tie in with the holiday season and a lead in to season 8, which was to begin only a couple of months later.