British Expats - Adelaide to Sydney

Hello everyone,
I am working in Adelaide at present for a large IT company. I am very bored (not much going on) and I am thinking of rather moving to Sydney to the larger IT hubs. I have discussed this with some of my Australian collegues and they only have negative things to say about Sydney.
I understand it is more expensive to live there (Adelaide is not exactly cheap these days either) with traffic jams and more crime but if it is so bad how come there are nearly 7 million people living there and only 1 million here?

Do you have to earn a fortune to live comfortably there? Is the crime bad? Is the trek to the city each day a nightmare? Do wages there make up for the extra cost.
How does it compare to London for cost of living?

Any help appreciated.