They seem to like anticipating the jokes people are going to make themselves. eg:
Angel Bob: We have no need of comfy chairs.
Phoebe: Heh, the scary angel said 'comfy chairs'.
Doctor: I made him say comfy chairs! :D
Also, from last week, I loved that the stupid 'two heads are better than one' joke became a plot point. And can't believe I didn't notice that.
The crack is a retcon monster!
The fandom is going to explode over that last scene. Glad I'm not really in it. It seemed very out of the blue for Amy, to the point that I'm wondering whether it's some effect of the Retcon Crack of Doom and that's part of why the doctor was all 'we've got to sort you out now.' It does consume time energy or whatever, after all.
Half expected the conversation between the Doctor and River to go:
Doctor: [You killed] a good man.
River: The best man I ever knew...
Doctor: ...oh bloody hell it's me isn't it.
(Although I'm not sure that's it. Too obvious, I suspect.)