The assistant director, Katie O'Rourke, appears in the film numerous times, generally in the background of a shot. She also appears, credited, as Finder's co-worker.
All of the LED signs, billboards, brand logos, and cell phone displays are computer generated, covering up existing logos and signs.
Look over Jane's shoulder in the close-up shot where she is talking to Finder on the phone. In the window behind her, there is a small sticker for a company called "Plausible Security." This label was also computer generated (replacing a "Honeywell Security" sticker).
There are a number of references to the characters from the "Tontie and Frooples" short film series by the same director, about a ex-Kindergarden teacher and her puppet companion who host a children's show. These references include Tontie and Frooples stuffed dolls carried by the young boys, a bumper sticker labeled "Tontie/Frooples '08" on a mailbox, and a billboard for "Tontie and Frooples: Live!"
This film was shot in September 2007, but it takes place specifically at 6pm on August 1st, 2007. If you look at the LED signs at each train platform you can notice this. The I-35W bridge span crossing the Mississippi River in Minneapolis collapsed at this exact time, killing 13 people. The director of this film witnessed the collapse from his apartment window.