Mathew Richmond's first name is spelled "Matthew" on the name plate on his desk (while it's not unusual for people to get things like that wrong, and order the wrong name plate, it's unusual for people to put up with it for long).
When Shawn leaves the bathroom (where Charlie is tending to his wound) she's seen in the bedroom wearing a long night-shirt with no pants. Seconds later she enters the bathroom with another shirt that's tucked into her pants.
When Shawn is on the roof drinking the vodka, the level in the bottle changes drastically from shot to shot.
When Shawn first goes out on the roof, she has the same dark lipstick as when she left her apartment. By the third or so scene on the roof, she now has light (or no) lipstick.
As Shawn and Charlie are escaping, Shawn turns the wheel to the left, as the car is turning right.
Film is supposedly set in Seattle, but features prominent Vancouver landmarks, as well as Canadian mail boxes and phone booths.