OK, major Doctor Who spoiler alert! Well, kinda-- not a plot spoiler, but a series 5 spoiler about the new companion.
OK, is that enough? Den of Geek is spreading the rumor that the new companion for the new Doctor is a young lass named Hannah Murray. I've not heard of her, but she was on a BBC show called Skins. She's very young, 19, which come to think of it was how old Rose was supposed to be in the first series (Billie Piper was actually 23 in 2005).
Anyway, consider this in the rumor stage. But it'll be a while before this one's confirmed, since the first of the last shows with David Tennant won't air until Easter, and the next one after that won't be until -- cripes! -- December! The rumor mill will have at least a year to churn, so expect lots of twists in this particular plot as time unfolds.