Actor Allusion: In the episode "Beers and Weirs", Bill says he always watches Dallas with his mom. Bill's mom is played by Claudia Christian, whose first acting job was on Dallas.
In "Tricks and Treats," Mr. Weir wears a vampire cape, a direct allusion to his sketch as Count Floyd on SCTV.
In "Carded and Discarded" Ken (Seth Rogen) exclaims "Canada" when given his fake Canadian ID, Seth is from Canada.
The Cast Showoff: John Francis Daley's accomplished dance moves were shown off during the mirror scene in "Looks and Books".
Creative Differences: According to one interview, Seth Rogen claimed that the reason the show never took off was because the TV executives all came from wealthy upbringings and, therefore, couldn't relate to the middle-class underdog mindset of the characters.
Dawson Casting: Averted by John Francis Daley (14) and, surprisingly, Seth Rogen (17). Downplayed with Jason Segel (19), Busy Philipps (19), Martin Starr (16), and Samm Levine (16). Played straight by James Franco (21) and Linda Cardellini (26).
Period Piece: Deliberately set in 1980-81 to avoid the tendency of teen shows to fall into this.
Retroactive Recognition: Perhaps as a testament to the show's potential, nearly every actor who was involved with it went on to lead a fairly successful career.
John Francis Daley has done a number of movies and TV shows, most notably Bones.
Samm Levine made cameo appearances in Apatow's next show, Undeclared and used Freaks and Geeks to convince Quentin Tarantino (a fan of the show) to cast him in Inglourious Basterds. Later on, he became a regular in podcasting, serving as the sidekick in Kevin Pollak's Chat Show and making frequent appearances on Doug Loves Movies.
Busy Phillips would join Dawson's Creek for its last few seasons. She would end up gaining greater acclaim as part of the main cast of Cougar Town, for which she won a Critics Choice Award for Best Supporting Actress in a Comedy Series.
On the production end of things, Paul Feig's later directorial credits include episodes of The Office, Mad Men, Nurse Jackie, and major films Bridesmaids and The Heat. He had only one other directing credit prior to Freaks and Geeks, although he'd been acting for years.
Screwed by the Network: The usual sad story. Aired out of order, shuffled around the schedule, barely advertised, and so on.
Sam Weir was originally meant to be tall for his age (as Feig had been).
Had there been a second season, Paul Feig wanted to have Sam breaking with Bill and Neal to find a new group of friends, Lindsay struggling with drug addiction, Kim Kelly getting pregnant, Bill's mom marrying Coach Fredricks and Neal's parents divorcing. And Sam would have gotten tall; John Francis Daley grew almost a foot in the year after cancellation.
Feig also wanted Lindsay and Daniel to eventually end up together.
On the topic of how Sam was supposed to be tall, Daniel was supposed to be Hispanic, and Ken was supposed to have long blonde hair. Neal was supposed to be named Art Thompson, Lindsey was supposed to be 15, etc.