Continuity mistake: When Lance and Seth Green are riding in the buggy, they are talking for a few minutes. During this time the side shot will show Lance with his arm all the way around Seth's back/shoulder. However, when the camera changed to a full shot, Lance's arms were at his side, nowhere near Seth's back or shoulder. This happened several times during this scene.
Continuity mistake: When the three of them are about to leave jail and Ian reads the message on his iPhone, the time says "August 14, 2008 10:02 PM". Later on, when Ian is in the car waiting for Ms_Tasty, the time says "12:02 Saturday, August 14". The date should be 15 August as it is after midnight (you can tell that this is late night/early morning as it is dark out and the time earlier was PM).
Continuity mistake: When Rex slams on his brakes after Ian tells him that he met a girl online, the background outside the driver side window is a building with trees around it. The shot then switches to the passenger side. When the shot goes back to the driver's side, the background outside of the window is just trees and other shrubbery, even though the car is still at a standstill.
Deliberate mistake: When Seth Green and Lance pull up to Ian and Felicia, the car being pulled by the carriage should roll a little bit after the carriage stops moving, but instead it stops on a dime when it is only being pulled by rope, and nothing else to stop it with when the carriage stops.