The character of Allison 'Ally' Stark was played by four different actresses over the course of the series: Krysten Ritter, Laura Clery, Lindsey Broad and Kate Micucci. The fact that different actresses were playing the role became part of the story dialogue in later episodes.
Mayim Bialik, who guest-stars as Doug's psychologist Dr. Bialik in several episodes, really does have a doctorate in psychology (specifically, a Ph.D in neuroscience) from UCLA.
Joely Fisher was only 13-15 years older than each of the actresses who played her daughter Ally on the series.
The exterior of the Stark's house was also used as the Kravitz's house in "Bewitched." In the pilot you can see the Stevens' house in the background across the street. The Stark's house exterior was also used for the Partridge family home and was remodeled after that show ended. The house used for the exterior shots for the Woodcock's home was also used as Tony Nelson's in "I Dream of Jeannie"
In the pilot, the caption "Day 8,743" pops up when the Starks are introduced. This means they have been married for nearly 24 years.