Hey,
I got some US Dollars attached to a Visa card, any huge benifit in buying say a new smartphone from a US online retailer (granted risks related to doa, warranty, etc) or just stick to buying locally from someone like Kogan or one of the many great bargains posted on this site :)
As you have guessed there are so many variables it's hard to say - I was in the US recently and planned to buy an iPhone 4S but after a lot of investigation it seems that the warranty issues are not as black and white as I'd like with many people finding their so called international warranty wasn't always what they'd hoped. I'd keep it local. Buy yourself a Kindle - they are a bargain compared to here.