Dawson Casting: Notably Averted: The character's stated and implied ages were reflected by the actors who played them, bar some exceptions: the actors who played Alice and the Guardian were in their late 20's.
The Danza: Ryan, though as it's most likely just a coincidence seeing how he's no more prominent than most of the characters.
Executive Veto: The executives refused to allow smoking to be shown. This (and firearms) were the only things that weren't allowed. This includes prostitution, slavery, underage drinking and attempted rape.
Real-Life Relative: Ebony, Java, and Siva, who play sisters on the show, are played by the real-life Cassie sisters.
Role-Ending Misdemeanor: The teenage actors playing Ved and Chloe in season 4 reportedly held up production by going AWOL for a whole day during scheduled filming hours. This annoyed the producers enough that both characters ended up getting McLeaned.
What Could Have Been: One has to wonder how the series would have gone if the producers didn't have to deal with the actors leaving so often.
Technology Marches On: Clearly the Virus struck in 1998, what with all the CD players instead of iPods being used and traded. Notably, the survival machines made by Jack and Dal in the first series were plausible.
Although CD players are easier to power than iPods, which need a computer to charge from. It cold be an ease of use thing.