A set piece used in Marie's Kitchen - a 3D plaster cast of fruit hung on the kitchen wall - comes from Jerry Seinfeld's apartment in Seinfeld (1989) (you can see it above the microwave in "Seinfeld" (1990) {The Pen (#3.3)}).
The living room no longer has a built in bookcase on the rear wall, it was only in the pilot. Where the bookcase was, is now the entrance to the basement.
Peter Boyle teaches Ally Marlon Brando impersonations. On Saturday Night Live, Boyle was in a sketch called "Dueling Brandos".