The episode is well known for this classic Joey-Chandler exchange:
Chandler: We have to assign heads to something [ducks or clowns].
Joey: Right. Okay, okay. Uh, ducks is heads, because ducks have heads.
Chandler: What kind of scary-ass clowns came to your birthday?
But it's full of good lines, some of them so casually delivered that it's easy to miss them. For example:
Chandler [struggling under the weight of baby supplies]: You know, I don't think we brought enough stuff. Did you forget to pack the baby's anvil?
Joey: Yeah, my uncle Sal has a really big tongue.
Chandler: Is he the one with the beautiful wife?
Phoebe also gets away with saying "sloppy seconds," but so quickly that it's easy to miss.
A few nitpicks: The episode is not particularly well-structured; Ross's allergy serves as the rationale for Chandler and Joey taking charge of Ben, but Phoebe's story has no relationship to the rest of the plot (great song lyrics, though).
And since when do city agencies use cloth diapers?
The episode is also notable for three guest appearances: Chrissie Hynde (who mercifully does not appear as "Herself"), Lea Thompson (crossing over from "Caroline in the City"), and Giovanni Ribisi (who was later cast as Phoebe's brother).