When Jack kisses Rose and the Doctor goodbye, John Barrowman made a special effort to kiss both actors in exactly the same way... except on one take, when he kissed Billie Piper as usual, then said his line to Christopher Eccleston, started the kiss, and didn't stop until they fell on the floor. (Source: John Barrowman on the DVD commentary)
The street corner at which the TARDIS reappears after being sent back to 2005 is the same street corner where Rose's father was originally struck by a car and killed in the opening of Doctor Who: Father's Day prior to Rose altering the circumstances of his death.
The trivia item below may give away important plot points.
Series 1 contained an underlying story arc about the meaning and identity of Bad Wolf, with each episode containing several references to the name. In this episode, Rose sees dozens of Bad Wolf graffiti, which lead her to realizing that she is the Bad Wolf, and uses the words to always lead her back to The Doctor.