Here's a couple of interesting trivia nuggets.
When Rose meets Clive who runs the Doctor conspiracy website Clive produces a drawing which indicates the Ninth Doctor was on hand for the erruption of Krakatoa. The Third Doctor, however, also states in the story "Inferno" that he, too was present for the erruption of Krakatoa in 1883.
And I don't know if this was deliberate or not but...
Clive also reveals that the Doctor was in the crowd on November 22, 1963 when Kennedy was assassinated. November 22, 1963 was also the day that the first episode of Doctor Who aired. Of course, due to the news out of America not many people bothered to watch the show and the BBC re-aired the first episode the next week.