Actor Allusion: In "Brotherly Love", Dorothy recounts how while on a double date with Stan and his Brother at a soda shop Stan "entertained" them by sticking straws up his nose and pretending to be a walrus. In the "Cousin Maude" episode of All in the Family, Arthur's character Maude recalls Archie Bunker doing the same thing on a double date with her Cousin Edith and herself.
One of the songs that Dorothy sings at the Rusty Anchor in the final season episode "Journey to the Center of Attention" is "Hard Hearted Hannah (The Vamp of Savannah)" (from Tin Pan Alley), which Bea Arthur had previously sung in an episode of Maude.
Corpsing: The reaction in the episode where Blanche gives the other girls calendars with erotic pictures. Apparently there really were some nude shots in there.
The questionable penis-shaped tin in the kitchen is actually a lobster.
Sophia's lack of tact is sometimes explained by Dorothy after the fact as the stroke Sophia had in the past which caused her to be placed in Shady Pines (though this is rarely referred to otherwise). The stroke and her propensity to say rude things was only fully described on the first episode.
The Other Darrin: Lots. From Dorothy's sister Gloria, to Blanche's daughter Rebecca, to Rose's daughter Kirsten, and even the cast of the episode that was a pilot for the spin-off series Empty Nest.
The Empty Nest example might not count, since the entire plot changed between Poorly Disguised Pilot and the actual series. In the pilot, the story was an older married couple learning to reconnect and begin a new part of their life after their youngest daughter leaves for college (an actual "empty nest.") In the actual show, the main character was a recent widower who's self-supporting adult daughters move back in (creating something of an Artifact Title.) The only connection between the two was the protagonist's occupation as a doctor and actor David Leisure, and even then, his character changed from a pilot named Oliver to a cruise ship employee named Charley.
Playing Against Type: Rue McClanahan and Betty White were supposed to play Rose and Blanche, respectively. They suggested switching around. Betty White was well-known for playing "Happy Homemaker" Sue Ann Nivens on The Mary Tyler Moore Show. Outside of her TV persona, Sue Ann was cruel and man-hungry, the antithesis of Rose. Rue, meanwhile, had played sweet but scatterbrained Vivian Harmon on Maude, as well as prissy spinster Aunt Fran on Mamas Family.
Rue McClanahan had previously appeared in a famous episode of All in the Family as the exhibitionist wife in a swinger couple whom Edith invites to the house after misunderstanding their personal ad.
According to Rue, this was a major reason that Bea Arthur agreed to star; previously, she'd told Rue that she had no interest in doing "Maude and Vivian meet Sue Ann Nivens."
Shout-Out: When Dorothy is working on the kids' show, Mr.Terrific has a puppet sidekick named Kolack from Twilar. This is very likely a shout-out to Danny Thomas, who appeared on a The Dick Van Dyke Show episode ('It May Look Like a Walnut') as "Kolack from Twilo." Tony Thomas, one third of the production team, was Danny Thomas' son.
The episode with the live chicken, Count Bessie, had to be rewritten slightly in regards to who was standing where during the scene, because Bea Arthur, despite being known as an animal lover, had a phobia about live chickens.