Trivia: The Special Edition covers of Return of the Jedi and Empire Strikes Back are wrong. The picture of the Emperor on ESB cover is from 'ROTJ', and the lightsaber duel between Luke and Vader on the cover of ROTJ is taken from 'ESB' (notice Luke is in his fighter pilot suit, and Vader is fighting him one-handed)
Trivia: Although credited to Leigh Brackett and Lawrence Kasdan, most of the script was actually written by George Lucas himself. He felt Brackett's draft got the tone and feel of the movie all wrong, and he rewrote the second draft from scratch. Kasdan's main contribution was to redo all the dialogue (admittedly a crucial element especially since Lucas is famously bad with dialogue), but otherwise nearly the entire screenplay was Lucas' work.
Trivia: The sound of an AT-AT Walker's footstep is a shearing machine used to cut sheet metal.
Trivia: There was a false page in the original script in order to fool all of the people working on the film. This was to keep it secret that Darth Vader was Luke's father. Only George Lucas, the producers and James Earl Jones knew the truth. Mark Hamill was told just moments before filming this scene so his reaction would be right, while David Prowse read the lines from the original script "Obi-Wan killed your father."
Trivia: When Lando orders the evacuation of Cloud City, a bunch of civilians run past the camera as our heroes go down the corridor. The very last guy in this group can be clearly seen carrying an ice cream maker.
Trivia: C-3PO's interruption of the kiss between Han and Leia was an ad-lib during filming.
Trivia: The scenes where R2-D2 is submerged in the mud pool were shot in George Lucas's unfinished swimming pool. Most of the crew were hidden under the water and the entire sequence was shot by Lucas himself.
Trivia: This is in the Special Edition of The Empire Strikes Back. Darth Vader returns to his Star Destroyer (just after the Millennium Falcon retrieves Luke from underneath Cloud City). The shot that is used to show Vader walking down the shuttle ramp and into the Shuttle Bay is from Return of the Jedi (different angle) when he enters the Death Star at the beginning. You can see Moff Jerjerod just before the end of the shot.
Trivia: In the movie, Jeremy Bulloch, who plays Boba Fett, is also seen out of his mask; namely as the Imperial officer who brings Lando, Leia, Chewie, and C-3PO to Vader's shuttle.