The "Bear" monologue that Trent delivers to Mike is almost verbatim something actor Vince Vaughn told Jon Favreau one night at a bar. Favreau liked it a lot and incorporated it into the script.
Nicole LaLoggia:
the film's line producer plays two roles: she plays Michelle's voice on the phone, and she appears as one of the bar patrons at the Derby (the brunette sitting to the right of Trent when Mike leaves the table).
In the first scene in Mike's apartment, the first time he walks into the kitchen, you can see a crew member reflected in the glass of the left kitchen door.
During the Rob/Mike apartment scene, in an over the shoulder shot (after he talks about the pain hurting less each day) Rob brings his hand up to his chin, but then in the next shot, his hands are on his lap.