I'll offer my experience on the tax thing. I spent about 4 months working in the Outback in 2011 after graduating college. Since I didn't stay long enough to qualify as a resident, I ended up being taxed at I believe 33 or 40% on the Australian side, so that royally stunk. However, that came back to the US on my taxes as a "Foreign Tax Credit" on line 47. Note that this is NOT a refundable credit. But, if you have 401k's or IRA's, you might be able to convert those and use the tax credit as an offset to those. That you might want to ask a CPA about, but I think it's right.
On the Australian side, I seem to recall that things seemed much simpler, although the rates were a bit higher, than US taxes. Further, because there are such an insane number of foreigners working in Australia temporarily, there are a huge number of tax places that will cheaply file for you. The worst part is that Australia's fiscal year ends in June or July and ours in January, so you have to file an extension or use a paystub instead of a more official statement of wages to file your US taxes.
I did my taxes myself for 2011, then paid $200 for a CPA through H&R Block to look them over, plus a little extra for their guarantee to defend in an audit. It wasn't really that hard, although I freely admit to reguarly reading 1040 instructions in my spare time for shits and giggles, so maybe you'd find it awful.
As far as Australia, do it, do it, do it! People were just so wonderfully friendly, a great culture and the weather in Sydney is pretty killer. If you're from Texas, Melbourne might be lousy, my impression was that it was quite gray and miserable for a good bit of the year. I found Adelaide to be terribly boring. Didn't make it to Perth, but it's quite far away. Remember that Australia is the same size as the continental US and Perth is basically the only major city on that side.
As an American, the thing that delighted and surprised me the most was actually how efficient and well run everything was. Granted, I was coming from Chicago, where things are anything but. But, it was my impression at least that their government runs well, people are engaged in politics (mandatory voting helps), everything is clean and nice in public places, very orderly. I haven't been to Scandanavia, but it really seemed to me to have that kind of well run efficiency that I have always associated with Scandanavia, with a wonderful amount of beer, sunshine, and happy folks.
One thing to remember on the salary/savings side is the mandatory 9%? employer contribution to your superannuation (retirement, similar to our 401k, I think the employer contribution might be going up soon or have recently gone up?), which you can then have refunded to you when you return to the US if you don't plan to return. Taxes were withheld on mine, but only because I was too lazy to file to get $50 or so.
Husband and I really hope to have a similar option in a few years. We basically figure if we can get our savings in line, we can go for a few years, let the savings just compound without adding as much, and enjoy the good life in Oz. So many places I wanted to travel to when I was there that I just couldn't make it to. Don't pass this up! :)