Just watched it, loved it really fun episode with great pace and I love the way it was told, with The Doctor skipping between timelines. However, I'm curious as to why Karen Gillan wasn't featured that much I don't think there has been a Christmas Special yet which featured The Doctor and his series compainion as the main characters (I mean The Christmas Invasion was more of a Doctor-Lite episode) I thought this would feature them both a lot more.
The thing that annoyed me most though wasn't the episode but the people on the DS forum who were watching, they were giving it no more than 10 minutes before saying either "Confused!!!!" or "Boriinnnnnnggg" it was really annoying that people would give time for the episode to develop.