In the line "I'm not liking what I'm typing; throw it all away," in "P.O. Box 9847," "away" is sung with a melisma (Bb G), musically giving something of a sense of movement.
I think the song is in G major (for the most part, the chord progression just alternates between G major and C major), but under the lines "I've described me very poorly, better try again," "I've been writing advertising; that's not really me," and "I'm not liking what I'm typing; throw it all away," there's an Eb major. This foreign tonality mirrors the narrator's dissatisfaction with what he's writing.
It's also significant that after the second verse, the narrator refers to what he's "been writing" (as if with pen and paper) but after the third verse, he talks about what he's "typing." In the same way that each verse accentuates different aspects of his personality, he uses different methods of composition.
