In the original script, Dawn was supposed to open the door of the Roman apartment and welcome Angel and Spike, but Michelle Trachtenberg wasn't available to appear due to her commitment to EuroTrip (2004). It was then decided to give Andrew the scenes which were originally planned for Dawn.
Julie Benz says her last appearance as Darla in the flashback scenes of this episode was "a great way for us to... say goodbye to our characters, to be together and to have some fun." She was relieved to shoot such a "playful" scene, "because anything else I think would have been too hard; too difficult; too painful." She adds the sheet she was wrapped in kept snagging on the camera dolly and falling down. "It was a great way to end; flashing everybody!" she says.
It is stated by a house-sitting Andrew Wells that Buffy and Dawn are living in Rome and Dawn is going to school there in order to learn Italian. This is an in-joke based on Kristine Sutherland who played Joyce Summers on Buffy the Vampire Slayer (1997). She was largely absent from season 4 because she was house-sitting in Italy, partly in order to allow her daughter to go to school there and learn Italian. Now her character's daughters do the same.
It is a commonly held but mistaken belief that the producers sought Sarah Michelle Gellar for this episode. Another actress played Buffy Summers in a faraway shot of her dancing with The Immortal in a nightclub. In fact, the intention of this episode was always that neither Buffy nor the Immortal would be clearly seen. Gellar was actually sought for the penultimate episode Power Play (2004), but proved unavailable because she was busy finishing the filming of Peace Out (2003). David Fury explains this in an interview with Mike Jozic:
"There was very, very little talk about that. No, she was never going to be in that. The missed opportunity to see Buffy was always going to be the joke of that. It's the tease of, they're going to see Buffy, and they can't quite get to her. It's sort of the After Hours (1985) kind of craziness where it's like, I can't get to her, I can't see her, and that was always pretty much decided. The person we expected to get and didn't get was Michelle Trachtenberg. We had expected to get her for that episode but she was tied up prepping a movie, I believe, and wasn't able to do it, which is why we brought Andrew back again. But, Sarah? No. We never expected Sarah to be in that episode. We did think she might be in the second last episode, "Power Play", just like Angel appeared in the second last episode of Buffy's finale. We thought we'd do that but wound up not".
Andrew's final scene in this episode (leaving for the Opera with two women while commenting that "people change") is at odds with the fact that Andrew was heavily implied (although never actually stated) to be attracted to men. Joss Whedon later admitted this apparent character change was due to this being a hold-over scene from when Dawn was expected to be in this episode (the idea being that Buffy's younger sister was now grown-up) and it was meant to be a mixed-sex group rather than all-female, but he wasn't there when it was filmed to make sure it was done properly.