David Tennant is the tenth Doctor and has ten in his name.
Peter Capaldi is the twelfth Doctor and has twelve letters in his name. (Funny thing is, so does David Tennant, but we'll just ignore that)
Before Harriet Jones became Prime Minister, nobody knew who she was.
Owen Harper is the only member of Torchwood Three that The Doctor never met.
Edit: Didn't realise I double posted.
The reason Rose smiles at the Doctor at the end of the Christmas Invasion when he says "Fantastic!" was not because it was the Ninth Doctor's catchphrase, but because in a deleted scene, he wasn't able to say it at first.
Watch the scene here.