This isn't directly about Friends, but it's kind of related.
Fans of Friends will remember that Phoebe had a twin sister named Ursula, who appeared in about 10 episodes throughout the run of Friends. The character of Ursual, however, originated on another NBC show called Mad About You, which starred Paul Reiser and Helen Hunt, and which premiered two years before Friends. Ursula didn't show up until the second season of Mad About You (about a year before Friends premiered), but Lisa Kudrow showed up in a season 1 episode as a blind date for Paul (Reiser's character) in a flashback episode. Interestingly, in Ursula's first Mad About You, she has two jobs: waitress and tour guide at the Museum of Natural History, which is where Ross worked on Friends (although the connection was never made on either show).
Anyway, having been reminded about all of the above, I started re-watching Mad About You. Not a bad show, and worth watching if you're a fan of Friends. Warning: it's VERY heavy on Jewish stereotypes and (at least the first season) VERY '90s looking. Also, Helen Hunt in her late 20s/early 30s, though was really hot.