When people know what they are supposed to do, like when Daniel knows he is destined to warn Charlotte, they can intentionally do otherwise. Like if I knew the future I could correctly predict if you’d think of an even or odd number every time as long as I kept it secret, but if I told you before hand it’d be even, you’d just pick an odd to prove me wrong.

Assuming Kate knows the “whatever happened” rule, she could ignore the threat to Ben and he would still survive if the rule held true, but for some reason she decides she has to act.

“Whatever happened, happened” is what Daniel always says, meaning it is impossible to change the past. But if Kate is going to extreme measures to save Ben (I’m assuming young Ben in Dharma times, maybe I should have said that), then there must be some danger that he could die. That means Daniel’s rule isn’t exactly right.
Also, given all the bad stuff Ben has done, you would think Kate would be glad he was dying. Her saving him makes me think there is some consequence beyond just his death. Kind of like in Back to the Future, if you create a contradiction (young Ben dies but old Ben is still alive) the universe ends. Something like that.

JACK: Is that what you call asking me to kill Ben while on the operating table? Make it look like an accident?
JULIET: [to Tom] That’s ridiculous.
JACK: She wants Ben to die. She said if I did it that she would protect me.
JULIET: Tom! He’s lying! I don’t know what you’re trying to do, Jack, but…
TOM: ENOUGH! Juliet, get out.
JULIET: Tom, he’s lying!
TOM: You said you can’t stitch him up — then you don’t need to be in here. Go Julie.
JULIET: Don’t let him fool you. He’ll never let a patient just die.

When will we see Locke again?
I want to see the 1950′s again!

I excited to see what happened to Aaron!