If it'll make you feel any better, it was announced on Thursday that season 3 of Sherlock will not film until 2013...
But it makes sense considering Benedict Cumberbatch is busy filming Star Trek and Martin Freeman is doing The Hobbit. Plus production of Doctor Who is expected to last into the new year.
The "Cumberbatch and Freeman are busy" excuse doesn't wash. Filming on
The Hobbit will wrap by the end of June.
Star Trek should wrap by September -- and even then there's no reason for Cumberbatch to still be filming by that point. (Eric Bana's filming was early in
Star Trek's shooting schedule. Same with Ricardo Montalban on
Star Trek II.)
The point is, as far as we know, the actors would be free to start on
Sherlock in 2012. So if
Sherlock isn't filming in 2012, it's not because of their schedules. It's because of Moffat's.