The first time Russell T Davies has written for 'The Doctor' since leaving 'Doctor Who'
Jo mentions Metebelis III when talking with Sarah Jane, which is a reference to her time in the original series. The third Doctor had attempted to take Jo there on his first Tardis trip after his exile on Earth was lifted, and would later visit the planet on his own at the beginning of Jo's last adventure, 'The Green Death'.
Continues the Whovian tradition of pairing "Smith and Jones"; as in Sarah Jane and Jo.