Much of the show's popularity derived from all the sex between the main characters. Many people think that when the writers finally relented and allowed the characters to get together, the show's ratings plummeted, but this is a misconception. The fact is, the actors had more sex once they were together. And because of the nudity, the ratings went through the roof! The third season's ratings were poor because the episodes were no longer as clever or creative as the first two seasons, Shepherd's scenes were limited because she was pregnant, and Willis no longer wanted to be committed to a TV series because he had instantly become an action-movie leading-man with star power. It was all these combined factors which doomed the show, not merely the fact that the two main characters got together romantically.
The third season became notorious for repeated delays of new episodes, as well as an excessive number of "filler" episodes (e.g. a Christmas story, a retrospective show, a Shakespeare spoof, and an episode focused on Miss DiPesto) that ignored the primary story arc. Much of this was due to scheduling because Bruce Willis had broken his shoulder skiing, and Cybill Shepherd was pregnant with twins. One episode opener during this period mentions these problems in a mock newsreel style.
Voice actor and stand-up comedian Maurice LaMarche auditioned for the role of David Addison Jr. and came close to getting the part. He got three callbacks, but was eliminated before the screen-test phase.
ABC and Cybill Shepherd originally wanted Harley Venton for the role of David Addison Jr., but show creator and writer, Glenn Gordon Caron, rejected him for the then-unknown Bruce Willis (both screen test were filmed - two scenes each with actress Mary-Margaret Humes playing Maddie Hayes - on 7 September 1984.) Venton's screen test, along with Willis's, appears at the end of the pilot episode DVD release.
Because of the trademark conversations/arguments on this show (mostly, but not always, between David and Maddie), in which two or more characters are talking at length simultaneously, the scripts for this show were typically two to three times the length of a script for a similar hour-long drama.
One of the hallmarks of this show was the irreverent (and frequent) way in which the so-called "fourth wall" was broken: at various times the actors would look directly into the camera and speak to the audience; dialogue referred to the "producers", "director" and especially the "writers" and/or "script"; and in the second-season finale episode "Camille", the characters actually left the set and went running around the film studio lot, then the episode ended abruptly around the actors when filming wrapped for the summer break (shown on-screen).
Bruce Willis made the film Die Hard while starring in "Moonlighting." By the time the series ended, "Die Hard" was available on VHS. In one of the last "Moonlighting" episodes, Willis and a love interest are seen walking past a video rental store while an employee is tearing a "Die Hard" poster down from the window.