California Doubling: The harbor the Minnow is seen sailing from in the opening credits (in the color seasons) is really the harbor at Newport Beach. The cave Gilligan sometimes hid in is located a little south from there, at Corona del Mar, and is still known today as 'Gilligan's Cave' by locals.
Descended Creator: Harold Hecuba was played by Phil Silvers, whose production company Gladasya ("Glad to see ya," get it?) made the series.
Determinator : A meta example in Sherwood Schwarz. Everyone hated the show when it was first pitched, right up to the original pilot, which was rejected by CBS. Schwarz plunged ahead despite all the negativity, and the show became one of the most popular comedies of all time.
Edited for Syndication: Syndicated repeats in the 1970s-80s had the ending theme with "each week" edited out, leaving "So join us here — my friends, you're sure to get a smile..." for fear viewers wouldn't know he show would be on again the next day, otherwise.
In the late 1980s, Ted Turner colorized the black-and-white first season for airing on TBS. Both versions are shown in syndication and cable.
Executive Meddling: One documentary made about the show reveals that the higher-ups had no idea why the show was popular and kept making changes; at one stage, they wanted Gilligan to gain a pet dinosaur.
I Am Not Spock: Happened to many of the regulars, Bob Denver especially, but Tina Louise (Ginger) never got over it. To this day, she pretty much refuses to speak about the show. Averted with Alan Hale Jr. who embraced his character and made numerous public appearances as the Skipper. Having already had a long distinguished career as a character actor, he was generally appreciative of a role that brought him recognition, especially among children.
Old Shame: Tina Louise was not on this show. Don't even try to talk to her about it. She was the only surviving cast member to refuse to participate in the animated series or the reunion movies, which naturally resulted in her being portrayed in Surviving Gilligan's Island as a vapid bitch while everyone else had no negative traits at all.
Louise seems to have mellowed out though over the years. On Twitter she occasionally makes jokes and references to the show (even noting in her description that she is "still living on an island (Manhattan)"), and she did occasionally attend reunion specials, and seemed to be having a good time. It's been theorized that the real reason she didn't take part in the biography special was because it was co-produced by Dawn Wells. The two actresses never got along well.
For many years, the entire first season was an Old Shame in regards to syndication, since it was in black & white (Seasons 2 & 3 were in color) and thus episodes from it were rarely aired because of a perceived preference for the later color episodes. TBS' efforts to "colorize" the first season episodes allowed many viewers to see them for the first time.
The Other Darrin: Ginger in the reunion movies was recast with Judith Baldwin, and then Constance Forslund. She was voiced by Jane Webb on The New Adventures of Gilligan and Dawn Wells in Gilligan's Planet.
Real-Life Relative: Bob Denver's son played Gilligan in a dream sequence version of Jack and the Beanstalk.
Recycled Set: Over the course of the series, two Western-themed Dream Sequences were filmed on the Gunsmoke set. To further lampshade the connection, a rescored version of the Gunsmoke theme was used as incidental music in both.
Screwed by the Network: Originally intended to have a fourth season, the show was cancelled at the last minute to make room for Gunsmoke. The latter was supposed to be cancelled, but was renewed at the last minute at the insistence of then CBS chairman William S. Paley, as it was the favorite program of Paley and his wife, Barbara Mortimer. Sherwood Schwartz was so furious that he took his next show to ABC.
Talking to Herself: Jane Webb voicing both Mary Ann and Ginger in The New Adventures of Gilligan. Dawn Wells would do the same for Gilligan's Planet.
The Other Marty : Ginger and The Professor were both replaced after the original pilot.
Unfinished Episode: A fourth season was planned, but cancelled at the last minute. Story treatments of the Season 4 episodes are available, though a TV retrospective suggested that actual scripts had already been written.
What Could Have Been: Carroll O'Connor tried out for the Skipper. Jerry Van Dyke was approached for the part of Gilligan. Dabney Coleman was considered for the (replacement) Professor.
Instead of Mary Ann, the cast in the first pilot included a blonde secretary named Bunny. Ginger was also a secretary instead of an actress, and the Professor was instead a high school teacher.
Jerry van Dyke turned down the role of Gilligan because he thought the concept of the show was too strange. Hilariously enough, he ended up playing the lead in the infamous My Mother the Car.
Word of God: Erika Tiffany Smith, played by Zsa Zsa Gabor, explained about the island and the Castaways, but couldn't offer the exact longitude nor latitude, plus no one could decipher her diary (which was written in Hungarian, which nobody in the Navy could read). The sailor who brought her could have told people but apparently, he "suffered a major coronary and died."