In the unaired original pilot, the character Alex was a native American and not played by Colin Hanks.
Katherine Heigl and Jason Behr were engaged in real life during the show. Later on, Katherine went on to star on Greys Anatomy (2004) and Jason on The Grudge (2004) where he met his future wife Kadee Strickland. Kadee went on to work on the spin-off of Greys Anatomy (2004) called Private Practice (2007)
The classic Liz/Max "Where are you from?" ... "Up North" scene appears to almost certainly have been inspired by, or intended as an homage to, the dinner seen in the cult SciFi film The Hidden (1987). The same question, answer, and gesture, appear in that dinner scene, involving Kyle MacLachlan, who also plays the part of an alien ("hiding" within the body of a human, unbeknownst to the other characters in the scene).
In 2021, Jason Behr played another alien on Earth in the final season of Supergirl (2015), appearing as Zor-El, the father of the show's title character and, by extension, Superman's paternal uncle.
In the Pilot Episode, Kyle wears earrings in both ears. In the the next episode, along with subsequent ones, he no longer wears them.