Actor Allusion: Whenever Perry's around, allusions are made to Richard Nixon. (Perry doing the peace sign, or a Watergate headline hanging behind his head, etc). Lane Smith played the 37th President in the television movie The Final Days.
At one point, he even compared Lane and Kent to Woodward and Bernstein.
Additionally, the mayor of Metropolis, played by Sonny Bono, makes references to his lyrics in his speeches.
Creative Differences: Deborah Joy LeVine, developer of the series, didn't want Clark and Lois to get married until the Series Finale; ABC felt otherwise, resulting in her being kicked off the show at the end of season 1.
Directed by Cast Member: "Season's Greedings",was directed by Dean Cain. His real-life mother, actress Sharon Thomas, has a brief cameo as the customer who gets into a fistfight with Lois over a toy doll.
Enforced Method Acting: In this version of the mythos, before Superman shows up, Lex Luthor is shown to be an adrenaline junkie, staring down cobras and punching out sharks. There was only enough money to film one of these scenes, and the snake wrangler evidently ate up the safety budget, so John Shea had to stare down a poisonous snake for real.
Executive Meddling: There were fights between the writers, the execs, and the fans as to whether Lois and Clark would tie the knot in the show. The results werenotpretty.
It also interfered with the comic book marriage which would have originally happened in 1992 but was postponed to coincide with the TV show marriage. The resulting gap in their story arc led Jerry Ordway (the then-current writer/penciller of The Adventures of Superman) to comment, "Why don't we just kill him?" The rest is history.
Genius Bonus: In the pilot, Clark crashes at the Hotel Apollo while he looks for work. The name is an intentional reference to his Superman persona. In Hellenistic times and especially in modern times, Apollo became identified as the god of the sun.
Fake Nationality: Patrick Sullivan is played by an English actor, hence the unconvincing brogue.
Fake Russian: A pair of fake Ukrainians in "Lucky Leon". (Including Mark Rolston).
Method Acting: You wouldn't know it just from watching him, but John Shea took Lex Luthor very seriously. Not only did he study Nietzsche, but he checked himself into John Jay College of Criminal Justice in-character to get a diagnosis on 'his' pathology. It's a wonder they even let him out.
Name's the Same: "Deathstroke" has no connection to Marv Wolfman's DC Comics supervillain — as if it weren't obvious enough by the fact he has magnetic powers, a different surname, and he's not missing an eye.
The Other Darrin: The notable changeover from Michael Landis to Justin Whalin (as Jimmy Olsen). The main issue behind Landis' removal was that he looked too old to be a believable Jimmy. And though he played the comedy well, he was a bit too cool to be Clark's sidekick.
Lois' family is completely overhauled from Season 2 onward. Harve Presnell and Beverly Garland take over the roles of Sam and Ellen Lane, respectively (it helps that Garland looks a lot like Teri Hatcher). Lois' sister Lucy is played by two women before dropping off the map altogether.
Terry Kiser plays H.G. Wells in two episodes out of four, with Hamilton Camp standing in for him as an older incarnation.
Jor-El is played by two actors (three if you count his silhouette in "Never on Sunday").
Inspector (Or Detective; the show can't decide) Henderson is first played by Brent Jennings, before undergoing a Race Lift with Richard Belzer. In the fourth season, he reverts to black again, this time played by Mel Winkler.
In a strange case of The Other Darrin and Name's the Same, there are two version of the Toyman in this series. The first, Winslow Schott, is a Child Hater named after the comic book Toyman's real name and is played by Sherman Hemsley. A second villain (this time explicitly referred to "Toyman") appears in Season Four, hews closer to the original comic depiction, that of a creeper who actually prefers the company of kids.
Jon Tenny, the original actor for Ching, was unable to return for the fourth season. He is replaced by Mark Kieley in the premiere episode.
And he follows it up with dating Bloodrayne. Seriously, what is it with Jimmy and these women?
Raymond's brother Robert used to be an unfunny clergyman named "Reverend Bob".
Bobby Singer once stole a scientists' invisible suits (maybe he needs them to help with demon hunting?)
Screwed by the Network: The series was actually a lock to return for a fifth season early on in the fourth, but the network wanted out (likely due to declining ratings). The series wound up being put on hiatus for a time, but when it came back, there was no promotion and ratings fell even further. Even worse, by the time cancellation was definite, the series was stuck with one heck of a loose end.
Throw It In: Right before the Closing Credits in "Ghosts" Teri Hatcher waves a spatula around and splatters (an offscreen) Dean Cain with egg goop. Her reaction was so funny that they evidentially chose to leave it in.
What Could Have Been: An earlier script for "Seconds" had Mindy Church team up with Lex to try and kill Superman, and being punished for her crimes.
Kevin Sorbo was in the running to play Clark/Superman. In fact, it was a toss-up between him and Dean Cain. (skip to 6:09 for the good stuff.)
Cain: I heard his audition, too. I was like, "Oh, I got this."
Lex Luthor was going to be the villain of "Soul Mates" instead of Tempus, but John Shea was filming something else and couldn't make it.
Written By Cast Member: Dean Cain wrote "Season's Greedings" and "Virtually Destroyed" (from a story by himself and Sean Brennan); Teri Hatcher co-wrote the notably Lois-centric "It's A Small World After All."