The movie was originally written with Salt as a male (Edwin A. Salt), and Tom Cruise was approached to play him. Ultimately, he backed out and the script was rewritten with a female lead and Angelina Jolie was cast.
The character of Salt is named for the Strategic Arms Limitation Talks (S.A.L.T.). The talks, in 1969 and 1979, were between USA and Soviet Union during the Cold War.
The true design of the Presidential Emergency Operations Center (PEOC), where the last part of the movie is set, is highly classified. So production designer Scott Chambliss based his designs on the old German government bunker in Ahrweiler, near Bonn.
It's never stated explicitly beyond "present day," but the main action in this film takes place "in the near future" after the movie's release (summer of 2010). Evidence: In a scene shortly before the vice president's funeral, a long shot of a TV newscast shows his date of death as 2011.