In my opinion, nothing was more shocking than finding out that Kate was raising Aaron as her own. That was definitely my biggest WTF moment this season.

P.S. So far, nothing has surpassed my all-time WTF moment, which was finding out that Locke had been in a wheelchair at the end of his first flashback episode in season 1.

I think Sayid working for Ben was the biggest shocker for me

I'm DYING to know who the "bad guy" is. Ben or Mr. Widmore?

Aaron and Kate.

But, and this may have been last season... the thing that has me reeling is Jack's change once he gets off the island. I can't handle it, it makes me so sad.

Sayid working for Ben. That was a shocker.

Sayid-Ben. That was just messed up.

I hope everyone saw this most recent episode because I don't want to spoil it for everyone but... Rousseau getting shot at the end of this past episode was a shocker for me!

Sayid working for Ben. I didn't see that coming.

for me it was Michael being Ben's mole

I don't think Jin is really dead, and I had a feeling about Michael, but I was totally shocked and awed when Sayid was working for Ben. I think I literally gasped out loud when I saw that.