I've driven quite a few thousand miles in Oz now and you certainly have to, er, keep your eyes open, especially on any 'blind' corners or brows.
Mind you, there is no excuse as with most change in speed limits (both up and down) you are warned well in advance, unlike here where it can suddely change from 60 to 30 with no warning.
Here, they seem to spend more on signs suggesting there are speed cameras (often there aren't any) without addressing the sudden limit changes that just gives the police the opportunity to use the mobile cameras knowing that they will get some unwitting offenders unable to knock off the speed in time.
Moreover, how many times have you driven in relatively built up areas not sure whether its a 40 or 30 zone, due the absence of roundels - honestly its a lottery half the time, unless you know the area well. Hence why I use a snooper that identifies 'high risk zones' that has helped me, (and no doubt a fair bit of luck) to keep a clean licence.