Billie Piper is leaving at the end of the season.
Certainly not the first companion to leave the series, but as so much of the flavor of the first two new-era seasons is related to her, sometimes at the expense of the Doctor, I'm interested to see what the next companion will be like and how the show adapts to accommodate him/her/it.
In other news, perhaps the most spit-take worthy headline in a while: "Stephen Fry Pulls Out."
Even though reports have been that his script has been punted from the first to the second and then to the third season due to the expense of the special effects involved, he now has withdrawn his submission because he doesn't have time to write it. This will be one of those production stories that will be told in excruciating, yet constantly shifting, detail for years to come.