I'd say visit the sites scully suggested for a good info base.
We moved to Sydney in April 2005. I was kind of indifferent - was DH that really wanted to live there. It was fairly easy move as there was just us, no kids, and we both had a one year working holiday visa (DH quickly got a job where he could get a 4 yr business visa) We also didnt have to worry about selling property etc as we were renting.
You really need to do the research on salaries. DH is a mgmt accountant and they're very much in demand, so he had no probs at all getting a really good salary. I'm in IT, and had sligthly more trouble but took contracting work to start with.
As far as living costs, not that much different but felt we were better off. On the other hand we were just renting(and the price of renting has shot up there lately) Travel is far cheaper, but house prices in Sydney - its still bl**dy expensive if you don't want to live out in the sticks. Get used to cockroaches too the little blighters!
Bills were cheaper in general as was petrol, but they take mahoosive amounts of tax off you. The weather was great in general but it can take its toll - our rental didn't have heating - they don't tell you how blinking cold it can get in winter and we huddled around an electric fire for months! Summer is debilitating when you have to get to work every day in 30 to 40 degree heat.
Food shopping - I found that more expensive and really missed English supermarkets just for the choice and the offers you get. However for eating out you just can't compare. Thats the only thing I really miss about Sydney - everywhere being BYO and the variety, cheapness and quality of the food. Didnt matter how cheapo the venue, we never had a bad meal. We would eat several times a week there without thinking and never bothered getting a takeaway because it was just as cheap to go out. Here, going out for a meal is a real treat because of the cost and always a bit hit and miss.
You tend not to get the benefits you get here with some jobs (i.e in my job here I get free private health care) and the standard amount of holiday is 20 days, and we were forced to take 5 of those at Christmas, which makes visits back to the UK hard. That was a big deal to me.
My DH loved the pubs - they are far more focused on sports and tend to have loads of TV showing at least three kinds, plus 'pokey' rooms if you like to gamble (although their pokey machines are sh*t) I loved the fact that they are really into hobbies - took up hobby ceramics and made friends that way. They also seemed to have a lot of food fairs and events within the community which was great - always something to visit even though they were always pretty similar.
If I think a bit harder theres probably loads more I could write, but it depends a lot on the location you want to move to. I really liked Melbourne, but possibly because I felt it reminded me of the UK, and the weather wasnt that great, so then what would be the point! Neither of us is a beach person, so that whole surfy lifestyle was out!
In the end though, there was one factor that brought us back, and that was family and friends. We were only there 15 months, but I could never detatch myself from them and you have to to a certain extent. Its not possible to visit every year unless you're loaded, and its too much to expect other people to use up their own holiday and vast amounts of money visiting you. Yes communication is easier than ever, but at the end of the day I always wanted to have a girly chat after a few drinks with my mates on a Saturday night - as this was Saturday morning for them wasnt quite the same!
Also the thought of having a child out there (I actually found out I was pg with our first 4 weeks before we flew back, so it wasn't a literal factor in the decision but it was considered when making that decision!) which wouldnt have any other family left me cold really. I wanted my family to be close (not necessarily down the road - but close enough to pop down to visit dc for a day or two)
I absolutely recommend trying it though if you can afford to do that. I am so glad that we did. As I said I never considered it but DH really wanted to, and we had a lovely time even though I never felt 'settled'. That may have been different if we'd bought our own home, but I doubt it. I have more confidence in myself now as I had to go out and find work (whereas here I'd had the same job since I left uni) and it did feel very 'carefree' living there - but the good weather contributed towards that since as I said, it can actually get quite cold from about April to October and it doesnt feel the same in those months!
okay, ramble over...