I didn't really have a great experience with taxi drivers in Sydney. One of them was too busy listening to the football to answer my questions, another was chatting on the phone to someone in a foreign language and most of them were just really bad drivers - racing up behind other cars and screaming to a stop.
Use common sense and you'll be fine. However, Sydney cabs are notorious. Pointers are: If you share a cab with other people, make sure the meter is on multiple fare or refuse to pick up extra fares. You can demand Airconditioning! If the driver stops to read maps, they must stop the meter. And worst, sometimes they will refuse your fare if you're not going in the 'right' direction, if that happens get a cab and say you want to go to the casino and then 'change' your mind about the destination.
Don't assume that because you get into a taxi, the driver will know how to go where you want him to. Quite a lot of taxi drivers are not native of Australia, let alone Sydney and don't really have a good knowledge of the city. the worst example I had was a guy who didn't know how to get to Harbour Bridge from a place not far from Circular Quay. Ok, there were a few one way systems to take into account but still. So, when you get into a cab, have a map with you, just in case your driver is totally lost.