Yeah, I have played with oanda before, but I'm not really into hardcore forex. I made a bit playing USD/JPY but it got boring watching graphs all day.
The other issue is that the "account" currency is not AUD, so any gains in USD may be wiped out once they're converted back to AUD. I guess there might be some AUD forex companies but I didn't come across any.
So my multicurrency account isn't really a gamble, it's just choosing the best time to convert.
Sometimes I'll hedge and convert half "now" then hold the other half if I'm not sure which way things will go.