Marge had to share her diary with her uncle when she was younger.
Lisa says she looks like a Powerpuff Girl with her hair blackened, specifically Buttercup.
When checking in at the motel, Lisa uses the psuedonym "Lady Penelope Ariel Ponyweather". These are seemingly references to:
Lady Penelope Creighton-Ward, International Rescue's London agent in the British sci-fi franchise Thunderbirds.
Ariel from the Disney film The Little Mermaid.
Possibly My Little Pony.
In some versions of this episode, the end credits have a scene where Bart sneaks into Lisa's room and steals her diary, then gives it to a sleepwalking Homer, only to shock him.
This is the second episode in the series to take place in Lisa's eight anniversary. The first was Stark Raving Dad.
In Homerpalooza, a doctor says that if Homer takes another cannonball in his gut, he could die. In this episode, Dexter Colt fires a man with a cannon to hit Homer and Lisa, but in order to save her, Homer stops the man with his tummy, which made Lisa apparently worried.
The quote by Carl of someone cobbling shoes for him after hours is a reference to the story The Elves and the Shoemaker.
Screaming Monkey Research Labs are mentioned again ("HOMR ")
When Bart beams the laser at Principal Skinner, the red dot on his pants, when he pulls them down and Chief Wiggum stops in his car in front of him, how can the laser still be beaming on Skinner if Wiggum's car is blocking out the laser? It is possible the dot shining through one of the windows, although that should at least weaken the dot.
To cause instant and permanent blindness requires at least a class 3B laser — massive overkill for a laser pointer (they are usually class 1 or 2), and extremely unlikely in a laser pointer small enough to be pocketable. Of course, it could be that Colt was simply dazzled or temporarily blinded.
When Homer and Lisa pass by the "bridge out" sign we can see all the way to the bottom of the sign up to the letter U in out. When the sign is viewed after the branch is pulled back, we can see that the O and probably V in the word "overpass" should have been seen in the first place.
A red laser pointer would not produce an actual beam (except in a very dusty, smoky or foggy atmosphere), it would only produce a dot where it was pointed.
Why didn't Homer simply tell Marge that the store was out of the diaries?
This episode won the 2004 WGA Award (TV) for Animation.
For the first time ever, we see what Lisa's hairline looks like in this episode when she colors it black. (Not counting 'Lisa The Beauty Queen' because she gets different hairstyles.)
Carl mentions that he has severe schizophrenia.
Fox announced that it had renewed the show until 2005 and its 16th season. This will make the series the longest running comedy series in US TV history save for "Saturday Night Live", and it will have beaten the previous record holder for longest-running primetime animated series (The Flintstones) by a full 10 years.
Homer's e-mail address is actually writer Matt Selman's e-mail address. Matt used to write back to fans as Homer until about a month after this episode aired. Later, the address was disabled due to too many sent letters.
The couch is Groening's version of the famous 1932 photograph "Lunch on a skyscraper".