I've found that /r/android and /r/askscience are among the best communities on Reddit, they're both generally very helpful and friendly. Was the Doctor Who Christmas special any good? I haven't seen it yet.
It's my favorite christmas special that the've done yet. Damned with faint praise, though - I haven't really enjoyed any of their christmas specials very much. It was a solid episode, that avoided the tendancy to feel "excessivly fairytale" that the last two christmas specials have had. My primary complaint was that I didn't buy the doctor's motivation for... what we will call the first half of the episode. (to avoid spoiling anything.) Not that I feel that such motivation is impossible, but it was seriosuly undersold.
I absolutely loved it. So many nods to classic who. I recommend watching it if you have the chance!