The Simpsons holds the record for most guest stars; it is also the only non-variety show to have had appearances from three former Beatles (Paul, George and Ringo).
The only voice artists who regularly perform as only one character are Yeardley Smith as Lisa and Marcia Wallace as Edna Krabappel. Yeardley has also voiced different versions of Lisa (Lisa Jr. and Lisabella) in at least two other episodes.
Initially, Yeardley Smith auditioned for the voice of Bart and Nancy Cartwright for the voice of Lisa. They play them the other way around.
The Simpsons continually pokes fun at the Fox network because it is the only show on Fox that does not have to be checked by its executives and edited accordingly. This also means the producers of the show can get away with a lot more on prime time television.
A running joke throughout the series is that no one knows where Springfield is. The writers are always coming up with ways to keep the audience guessing. Some examples of this are: in 'Sunday, Cruddy Sunday' when Marge phones the egg painting company and gives her address, she says, "742 Evergreen Terrace, Springfield Ohi...", then cuts out to say, "Oh hiya Maude!" to Maude Flanders, who suddenly appears in the kitchen. When Homer and Bart are off to the Edison Museum in 'The Wizard of Evergreen Terrace' they drive past a sign with exits to New Jersey, Michigan and Oregon, none of which are close to each other. When Larry Burns spots Mr. Burns on the train, he asks where the train is going. The conductor says, "Springfield." and Burns asks, "Springfield where?", but the conductor's reply is drowned out by the train's engine.
Bart's anonymous prank calls to Moe the bartender were inspired by tapes of real-life prank calls made to New Jersey bartender Louis "Red" Deutsch (the tapes were widely circulated during the 1980s). Deutsch constantly received calls requesting fictitious bar patrons (Al Coholic, Stu Pitt, etc), and always responded in a hostile manner every time he realized he'd been duped.
The Simpsons are named after Matt Groening's own immediate family. His parents are called Margaret and Homer, and he has sisters called Maggie and Lisa. Bart is the only one not named after a Groening, although he takes Matt's place in the Simpson family.