These past few epsiodes have been fantastic. I had become very annoyed that everyone seemed so hesitant to take an action because of some mystical potential repurcussions. When Locke shoved pirate-man into the sonic weapon, that pretty much satisfied me.
I didn't think anyone was surprised by the revelation that Jack and Claire are brother and sister. As Exiled_devil notes- we saw Christian arguing with a blonde woman in australia about seeing his daughter in season 2 (in an Ana Lucia flash back). I thought the twist in the episode was that it turns out the woman he was arguing with was Claire's aunt, not her mother.
But the hair: It's a device to fix the Claire flash back in time. Since that flash-back she's grown out her hair, and had a baby. In other words, a long time passes between her accident and boarding flight 815 - probably several years. Until we see a pregnant Claire apologizing to her comatose mother - I had assumed she recovers (because of the scene in the A_L flashback).
Then again, the hair might also be part of the black & white theme they've played with (eg, Locke playing backgammon with walt). When Claire had black hair, she was a bad daughter. When we see her with blonde hair again, she's repented and is now moving into the next phase of her life: a whiney mother who's way of pronouncing "chah leee" and "oh kaaay uh" irritate me to no end.