Everytime I go to Sydney I HAVE to catch a ferry to Manly and spend a few hours there, particularly if the weather is good. I also HAVE to go shopping at QVB
I second the ferry to Manly. Get Max Brenners while yu're there... fish and chips on the beach (along with teenage making out ), and then ice cream from the little ice cream shop on the way back...

but, if you're PTing get daily passes... it's expensive. we spent forty dollars on one days pt in sydney and we caught two trains and a ferry