Yes. It's true. Sherlock series 3 is not filming in January 2013, but has been moved to March.
Sherlockians are already on it, at least in fan art.
There was panic, grief, and anger across the Interweb during the 24-36 hours while the rumor of later filming flew across the world.
Do be patient! Remember that our boys are famous now, and they do have other responsibilities, thanks to Sherlock. We'll get them in The Hobbit and Star Trek. And in Benedict's case, in a lot of other roles.
If you happen to be curious about how filming went for series 2, Sherlockology has a post about that. A rough guess suggests that the UK would have Sherlock series 3 about six months after filming.
Some other fan art: The adversaries in suits. Dear Jim to Santa Claus.