The only film in the series not to feature Arnold Schwarzenegger, who was unavailable due to serving as the Governor of California at the time. Instead, bodybuilder Roland Kickinger was used for T-800's brief appearance, with Schwarzenegger's likeness digitally superimposed.
Old recordings of Sarah Connor are played in the film, with lines nearly word-for-word from The Terminator (1984). Linda Hamilton voiced the lines herself in an uncredited role.
(at around 28 mins) The trick with keeping a shotgun attached around the arm that Marcus shows Kyle Reese, is used by the older Kyle Reese played by Michael Biehn at the beginning of the original The Terminator (1984), after he saws off the butt to shorten the shotgun he stole from the police squad car.
Special effects wizard Stan Winston died during filming (15 Jun 2008), making this the last film he provided visual effects for.
Helena Bonham Carter lost four members of her family in a car crash. As a result, filming was halted indefinitely so she could return to the UK to tend to her family.
Stan Winston: You can see him briefly as a white-haired prisoner on board the harvester after the petrol station raid.