Having lived in Ho Chi Minh City for almost 7 months, I'm sure I can give you a fairly good run down on it. Its hot. Everyday. Hot. Rainy season has just started (June to November). Before that we had the hot months of Febuary, March and especially April, which was suffocating. I think its the hottest place in Vietnam.
Everyone is up and about exercising on the city streets at sunrise - that is, 4.30 in the morning. After 11.00pm, the city sleeps. These times are true except for a small minority (that I am part of).
Commuting in the city is asking for hospitilization, but everyone does it anyway, you don't have a choice. There are thousands upon thousands of bikes jostling for space - combined with the exhaust fumes, the honking horns the beating sun and trying to stay alive, it can make quite an intense experience. During rush hour, it borders on ridiculous. Roads in HCMC define the saying - 'The only rule is : There are no rules'. Motorbikes are king, and a trip in a taxi is agonisingly slow, as the driver has to take ultimate care not to knock any bikes down - they don't stop, not even for red lights!