Have been toying with the Idea of Emmigrating there for many years (and recently went to a number of emmigration specialists to discuss stuff)
I've also family there/friends there and have been for an extended holiday to sydney, Queensland. I've also been an avid reader fo the many Aus forums for many years.
Some things to throw into the positive mix when thinking of going (and these don't necessarily put me off - but definately have put others off and made them come back from what I can see)
1.) The TV is generally poor compared to the UK. And yes, you will have to watch it at some point no matter how much people tell you that you never stay in (although you can get Premiership matches and Coronation street should you be that sad)
2.) As was said - Cars are expensive (but hold there resale / 2nd hand value)
3.) Cost of living is VERY expensive. Grocery shopping is extortionate, as are household Items and Mobile phones - as most things are imported.
4.) Energy prices are rising fast - as is the cost of things like Insurance.
5.) The jobs market in Aus is getting pretty dire (apart from Mining jobs)
6.) The tourist industry is quieting down a bit - which is affecting the economy in specific places.
7.) If you are moving to Queensland/Perth or other potentially remote places - expect to have a bit of a culture shock - and expect the jobs market to be even tougher.
8.) Waiting lists for medical problems is ridiculous in places. You also need medical insurance for dental work and ambulance bills.
9.) Spiders / snakes stories are designed to scare away Poms

You rarely see any and it is seriously overhyped. Stuff in the water however can be a real danger.
10.) Again, grocery shopping is a pain - as there is limited selection in most towns / suberbs - and the stuff on offer is no where near as good quality as the UK.
11.) Town planners build every estate virtually identical - which can be boring to look at and very tedious to live in after a few years.
12.) Yes - Australia does actually have cold & wet weather for a lot of the year in a lot of the states - It isn't 24x7 sun all year...... This year has been a very wet winter in a lot of states and a lot of Poms that went over have been very depressed with the weather.
13.) Run down areas of towns / Cities are severly run down - and drugs seem to be a bigger problem in those areas than they are in comparable areas int he UK. Just my take though.
14.) It's difficult to get any sort of finacial help for the first few years after emmigrating should you need it. You are also taxed in Australia on any money / savings you have stored in the UK. So if you sell your house in the UK / rent your house out in the UK and keep the money there - you still pay Aus Tax on it.
15.) Most banks charge for current accounts / ATMs are charged. Most places don't give a credit card until you are employment.
16.) As was said - don't expect effeciency or professionalism in most business that is important to you. People are very-laid back most of the time - they get the job done properly - they just do it in a different way/time-frame to the UK businesses.
17.) Household bills will be massive to what most Poms are used too. Factor in big Household Insurance bills, BIG medical Insurance bills and things like Pool Maintenance. Even if you are getting $100,000 a year - if you have a family, you may very well have less money for 'fun' every month than you had in the UK.
18.) Houses are cheap for what you get - but are generally not as well made or Insulated. Getting use to the design of Australian houses (usually open plan) can also be a pain for some people.
And this from a few days ago....
http://www.bbc.co.uk/news/business-14486128
Hope those don't put anyone off though