I love running gags and in-jokes, and I am often impressed when a piece of media manages to keep track of the little threads of them over time. One of my favorites is the Beetlejuice gag from Community, which took three seasons to pull off. Archer does a great job of not only tying them in over time, but making them circular within a single episode. It's a great challenge as a writer, and one I try to fit into my own writing whenever I can.