Cast Incest: Inverted. Real-life siblings Kristen and Eddie Alderson play unrelated characters. A few years back, a storyline involved Eddie's Matthew having a crush on Kristen's Starr. The boy had to pretend to have a crush on his sister. Gross.
The Cast Showoff: Several actors on One Life to Live. For instance, the original actor who played Jessica, Erin Torpey, has a nice singing voice, so they had Jessica in a band at one point, and also had her sing on a few other occasions. Evangeline Williamson got to sing a lot in the show, because her actress Renee Goldsbury is a real life singer/song writer, and was on a Broadway musical. And Blair Cramer, is also shown singing on a number of occasions, because Kassie De Paiva is a singer and has albums out.
Fake American: Susan Haskell (Marty Saybrooke) and Nathan Fillion (Joey Buchanan) are Canadian.
The Other Darrin: Lampshaded hilariously during the Vicker Man premiere - Blair is asked how she feels about being played by an Asian-American actress in the movie; cue to the cast credits, where the actress credited as Blair is Mia Korf (the Asian-American actress who originated the role of Blair Cramer).