Agency nursing in Australia can be good money.
Not all shifts are guaranteed; quite often you are booked and shifts are cancelled, (as patients get discharged, etc).
You can usually choose what days/hours you want. If you work weekends though you will get put in a higher tax bracket, so it may not be worth it.
Some agencies are great; others suck badly & are extremely inflexible. They have c**p attitudes & expect you to drop everything and run out to a shift (yeah, great idea if you have little kids!) Some try to push you into working on your days off and to travel further and further when you don't really want to.
When you join an agency, be firm. Tell them EXACTLY what you want, and ensure they record it (ie: I don't want to work weekends etc). Then they can't turn around and say they didn't know (I've had some nurse managers at agencies say things like this to me). Insist on good wages, after all, you are on call and that can be very inconvenient. And you ARE helping the hospitals out by going to their shifts.
I would recommend Mediserve - they are in every state/territory & capital city - fantastic & very understanding consultants. Their website: http://mediserve.com.au
Some nurse agency managers are too psychotic for words.....just do a few shifts with a couple of them to test them, then if they you bad, tell them you are leaving as there are PLENTY of nursing agencies - some also pay better than others, so ring them and ask them what their pay rates are.