Just a quick note to remind people who happen to have an Amex card: if you use it to get amex points, you can exchange them at American Express for foreign currency *and* at a better rate than if you redeemed the points for gift cards or products. For example, if you had 36,000 points you could get $250 worth of vouchers *or* currency equivalent to AUD$300. Even better, if you have a platinum or better card, make sure you show that - when I did last time I got a better exchange rate and no fees deducted.
Frankly, even if you weren't planning to go overseas, even taking into account the losses during conversion you may be better off getting the cash and then later exchanging it back for $AUD rather than getting gift cards!