When it comes to the Great Intelligence, "The Snowmen" appears to be an origin story. It started out tied to the snow, but after decades of association with Simeon it evolved to the point that it could transcend physical form. It then apparently made its way to Tibet in the 1920's or 1930's (I can't remember the details), and, then, the London Underground in the 1960's.
Kara, it was revealed in "A Good Man Goes to War" that Madame Vastra had been awakened from her stasis chamber by men digging the London Underground in Victorian England, and the Doctor befriended her there and got her to reconcile with the apes ruling the planet (the fact that she fell in love with Jenny undoubtedly helped). In that same episode, the backstory of Strax was that his clone batch had disgraced itself and the Doctor came up with the idea of Strax working as a nurse as penace. The Doctor then later collected Strax as part of his team to free Amy from Demon's Run, Strax was killed, but, apparently, Vastra was able to revive him and he traveled back to Victorian England to join her group (and play a hilarious comedic foil to the Doctor).








It was a whole lot better than last year's Christmas episode (which sucked).
I liked that The Doctor was hanging out with a Silurian and a Sontaran in Victorian London. I hope we see more of those characters as I am intrigued by how they got where they were.