Interestingly, I had this conversation with a friend who I recently got into Doctor Who, while he was still in the middle of the third season of new Who:
GEOFF: "So, how come the Doctor can never land his TARDIS where he wants to? Or, for that matter, how come sometimes he can't and sometimes he can?"
ME: "It's dramatic license. If it works for the story, he can land it. If it's funnier, more entertaining, or more dramatic, then he can't land it so well."
GEOFF: "Well, I have a theory. In 'Boom Town,' it's established that the TARDIS is actually, in some sense, alive. Is it possible that the TARDIS is actually deliberately guiding the Doctor where he needs to go, regardless of where he thinks he needs to be? The TARDIS can probably see all of time and knows better than even the Doctor about where to go. Has that ever been discussed on the show anywhere?"
ME (pause): "That's a brilliant theory! No, it's never been discussed in new Who, and though I haven't seen a lot of classic Who, I think I would have heard that idea already from fans if that was a commonly understood concept. But maybe it's true!"
When I posted that to some classic Who fans this week, they corrected me. The theory has been floating around since the 1964 episode "The Edge of Destruction," when it was revealed that the TARDIS is sentient. Still, as of last week, I had never heard anyone but Geoff say that.
So imagine how my jaw dropped when I heard this interchange (paraphrased from memory):
DOCTOR: "You almost never take me where I want to go."
TARDIS: "No, but I always take you where you need to go."
My friend called it! Kudos to him for figuring it out, and kudos to Moffat and Gaiman for going that route with the story.
BTW, has anyone else read the Doctor Who comic "The Forgotten"? It explores some very similar thematic ground to this episode. I highly recommend it.