Some news about Zaheer Khan is that he was running in faster and trying to 'hit the pitch' under the instruction of Wasim Akram who told him that he had to do that to succeed in Australian conditions. I don't have a source for this so take it with a pinch of salt.
He has looked really good in this test so far. Give him helpful conditions, and I am confident that the Aussies will be very wary of him. I was not at all impressed with RP Singh. Even the wickets he took were more of the batsmen making stupid mistakes. He was just overpitching it giving the batsmen easy pickings. He wasnt hitting the wicket hard, and wasnt troubling the batsmen. I think we need Ishant in place of him for Sydney (or Irfan)