When Frasier is confronted by a vision of every woman he's ever dated, the crowd of women at the cabin door includes nine actresses who have appeared in previous episodes as romantic interests for Frasier -- Tushka Bergen, Lisa Darr, Lindsay Frost, Cynthia LaMontagne, Gigi Rice, Claire Stansfield, Shannon Tweed, Lisa Waltz, and Claire Yarlett.
When Nanette sings "Bangladesh, Dhaka Before The Dawn," Frasier sarcastically comments, "The Bangladesh part's coming." Bangladesh gained independence from Pakistan in 1971 and, given that Frasier recognizes the song, it would appear that he and Nanette met around the same time. This would also correlate with Frasier's age as presented in Season 1. As of this episode, Frasier should now be around 47 or 48 years old.
Referencing a "Cheers" episode (Cheers: Diane Meets Mom (1984)), Diane mentions that Hester Crane tried to have her killed.
The title "Don Juan in Hell" refers to a play within a play that occurs in the play "Man and Superman" by George Bernard Shaw written in 1903.
Diane says to Frasier's mom, "You tried to kill me." Diane is referring to the events of the "Cheers" episode "Diane Meets Mom" (1984).