When giant Mojo Jojo rips open the side of the building he's climbing with the Powerpuff Girls in tow, it shows the interior of the second floor of Cartoon Network studios with caricatures of the actual employees.
According to the Hollywood Reporter, the principal voice actresses Cathy Cavadini, Tara Strong and Elizabeth Daily went on strike because they felt they weren't being paid enough to do a movie, so Cartoon Network threatened to replace them with more popular voice actresses for the movie as well as for the TV series. Fortunately, a deal was made and Cavadini, Strong and Daily were able to reprise their respective roles as Blossom, Bubbles and Buttercup.
The plans for Mojo Jojo's "make the city a better place" machine have the serial number "PPG-801." This was Cartoon Network's advertising campaign for the movie before the release date was bumped up. Originally, the film was set to release on 8-01-02 (August 1st). Numerous other references to 801 appear in the film.