Trivia: Possible Spoiler: At the time of this writing, it is generally believed that the "Mister Saxon" referred to throughout Season 3 will turn out to be The Master. One piece of evidence backing this theory is The Master's penchant for anagrammatic aliases: Mister Saxon is an anagram of "Master No Six," and if it's true, John Simm would be the 6th actor to play The Master. [Russell T Davies (who wrote most of the episodes) has said that the anagram is pure coincidence which was picked up by some people, but was completely unintended. Still interesting regardless.]
Trivia: When the Doctor sends the banknotes flying out into the street, all of the notes have David Tennant's or Phil Collinson's (the producer) faces on them, with quotes from the Fourth and Tenth Doctor (like "no second chances - I'm that sort of a man"). The notes have since become collector's items, selling often for about 50 pounds each.