Their choice has highlighted Vietnam's policy of simultaneously courting capitalism while maintaining ties with its one-time communist allies.
Japanese companies are some of the largest investors in Vietnam. Canon, for example, makes half its computer printers here.
Sachio Kageyama, the director of Canon Vietnam, says the company chose Vietnam for obvious reasons.
"Firstly, there's a very stable political situation here plus very stable economic growth and also a very intelligent workforce. These are big advantages in Vietnam."
Partly to facilitate such investment, the Japanese government is one of the biggest donors to Vietnam - building the country's biggest road and railway bridges.
But at the same time many parts of Vietnam's communist system maintain friendly links with countries who were once allies against what they regarded as Western imperialism, among them North Korea.
Last month, Vietnam's ministry of defence presented a bouquet of flowers and a special card to the North Korean leader, Kim Jong-il.
The army regularly sends comradely greetings to Pyongyang.
But perhaps something of greater geo-political significance was the discovery, last July, of 10 North Korean accounts at Vietnamese banks.
Reports at the time suggested that most of them were held at the army-owned Vietnam Military Bank.
The US Treasury's Under Secretary for Terrorism and Financial Intelligence, Stuart Levey, visited Hanoi.
Significantly, when they were faced with the choice of losing US support for their membership of the World Trade Organisation or ratting on an ally in communism, Vietnam's leadership chose the WTO and closed the bank accounts.
When it comes to security, though, Vietnam's main allies continue to lie in the former communist bloc.
Until 2002, there were still Russian troops based at the Cam Ranh naval base in the south of the country.
Despite their withdrawal, Vietnam continues to rely on Russia for most of its arms purchases.
The country is currently spending more than $1bn on new missiles, warships and other military from Russian suppliers.
But perhaps more sinister is the recently-announced internal security training programme between Vietnam and Belarus.
In January, the head of Belarus's interior ministry, Vladimir Naumov, was invited to Vietnam to discuss plans for future co-operation.
On his return he said that Vietnam was interested in acquiring "special technical materials" from Belarus - a phrase the authorities there use to describe crowd-control equipment such as truncheons, tear gas, electric shock weapons and personal armour.
When asked why, of all the countries in Europe offering police training, Vietnam had chosen the one with the worst human rights record, the government spokesman, Le Dzung, was frank.
"The co-operation against terrorism requires us to diversify our co-operation and learn from the experiences and lessons from as many countries as possible," he told a news conference last week.
"Anti-terrorism is a technical issue that has nothing to do with human rights."
But there is much more to Vietnam's ties with its former communist allies than security.
Central and Eastern Europe is home to tens of thousands of Vietnamese who went to work or study there during the Cold War and never went home.
The legacy can be seen in Hanoi in the long queues outside the visa offices of the Czech and Polish embassies, among others.
None of the people the BBC spoke to outside the Czech embassy were willing to give their names for fear of jeopardising their visa applications, but their stories show how long-established the ties are.
"I studied in Ukraine and worked in the Soviet Union and Czechoslovakia," said one middle-aged man. "And I'm here today to get a visa to visit my wife and children who have been living in Prague for the past eight years."
Several women who were at the front of the queue were hoping to find work in the Czech Republic and all had friends who were already employed in factories or homes there.
Even today Vietnam feels a special bond with those countries that supported it during the war against the US-backed south and with leftist parties around the world.
Fidel Castro of Cuba is highly regarded, as is Hugo Chavez of Venezuela. But in both these cases - feelings of comradely unity can be trumped by the motivation of hard cash.
Cuba, Venezuela and Vietnam have recently announced a joint venture to make fluorescent lights.
But the quantity of investment pales into insignificance when compared to the amount of US, Japanese, South Korean and Taiwanese cash currently flowing into Vietnam.
The hearts of many in Vietnam's administration may still lie in socialist brotherhood but their financial heads face firmly in the opposite direction.