The episode itself is a fairly straightforward example of the "pretending to be married to get rid of an old sweetheart" plot, which has been done on many shows before and after. (Frasier had Daphne pretending to be married to Niles to get rid of her fiance from England, and so forth.) It also gives guest star Hoyt Axton a chance to do some singing, but the episode is actually stolen by a non-actor: stage manager Buzz Sapien plays the role of the man in the elevator in the next-to-last scene, and runs away with the scene. MTM shows loved to have some random stranger saying strange things during a climactic scene; when in doubt about how to make the wrapping-up scene funny, put a wisecracking bystander into the mix.
Other than that, I think my favorite bit in the episode is Johnny's stream-of-consciousness repetition of everything Jennifer tells him when she's showing him around her kitchen. Also, Herb's nightmare about being attacked by a bunch of little Johnny/Jennifer children.
For those keeping score, this is the second of at least three episodes with Hare Krishna jokes. Hugh Wilson must have had a thing for that particular joke.