Newhart/YMMV

Ensemble Darkhorse: Peter Scolari's Michael Harris was written as a one-shot character for a season 2 episode, but the producers liked him so much they brought him in as a regular for season 3.
- Same with Larry and the Darryls, who were one-shot characters for the second episode and brought back little by little, eventually replacing Kirk as the Loudons' next door business men.
Flanderization: This show was never exactly realistic, but by the end it was basically a live action cartoon. The later seasons are far more acclaimed than the earlier ones, making this a rare example of a show improved by flanderization.
Foreshadowing - In a last season episode, Jack Riley, aka The Bob Newhart Show's Eliot Carlin, shows up as an unnamed man seeking psychiatric help for his deep neuroses. Could another reality have been invading, trying to Wake Bob Hartley Up?
Retroactive Recognition: Lisa Kudrow (Pheobe from Friends) as the wife of one of the Darryls in the final episode.