|BEWARE THE GOVERNMENT
Most countries now have legislation where the balance in a dormant bank account is turned over to the government. They'll seize an account if it has been dormant for more than:
10 years in Japan
15 years in the UK
In the USA, each state has its own rules, but the state of Georgia has lowered the period where an account if untouched can be seized to just one year.
Australia passed legislation last year to reduce the threshold on seizing dormant accounts from seven years down to just three. And in 12 months after the legislation was passed, the Australian government seized a whopping 80,000 accounts totalling A$360m!
In New Zealand, money in some bank accounts will be handed over to the Inland Revenue if it is not touched for 6 years. However, if the bank where the money is deposited is a "savings bank", which the major ones all are, then the account can go untouched for as long as 25 years.
Individual banks also have their own policies regarding dormant accounts. HSBC bank, for example will confiscate the balance of your account after 12 months of no activity. However that is not as scary as it sounds because the bank will make an effort to contact you first.
Lesson - make sure you keep your contact details up to date and if you have an Aussie account don't just let it sit there for three years without initiating some form of transaction.