Matt and Karen appeared as themselves with Matt in costume on the Tardis set at this year's BBC Children in Need. They greeted a couple of young fans who had suffered from meningitis when they were younger, and treated them to afternoon tea. I found it a little bit awkward for the adults, who I thought did a sterling job of being themselves and kind of being their characters. Interesting to hear Matt refer to the Doctor in the third person.
Long trailer for the Christmas episode, too!
SPOILERS (which I obviously couldn't spell in the thread title!)
Here's the clip: http://www.youtube.com/watch?v=lJCiXMDXbtc
Long trailer for the Christmas episode, too!

Here's the clip: http://www.youtube.com/watch?v=lJCiXMDXbtc