The end title designer forgot to use punctuation when writing the end credits. This resulted in all assistants being listed as "ass designer" or "ass painter" etc.
Ewan McGregor has said that the script never named his character, so in his head, his character name was Gordon McFarquhar. The credits simply list him as The Ghost (the character is never named in the original novel).
Lang's beach house set was built entirely in a studio. The Cape Cod views through the windows were the result of greenscreens.
It was originally filmed and rated as an R-rated thriller but, upon its purchase for U.S. distribution, it needed to be cut down to PG-13 to ensure a wider audience. This was done by cutting out eighteen "f" words, three "c" words, and some graphic sexual dialogue, as well as trimming some CGI blood spray during a death scene.
When Roman Polanski was arrested September 2009 in Switzerland, post-production was never put on hold. He oversaw every step of the film and made all of the artistic decisions. He finished editing the movie while in a Swiss prison. In December 2009, Polanski was released on bail but placed under house arrest, where he remained when this movie was released.