Thank you all for your kind words. A few comments about masks and helmets:
Most girls riding motorbikes in Hanoi seem to wear these masks. They are available in any colour and a lot of patterns. I was surprised that the woman in the photo didn't wear a pink one, since everything else is colour coordinated. The purpose of the thing is probably a mixture of protection against pollution and bad smells in general, protecting the make-up, and last but not least: it has become fashionable to wear them.
The hat is actually a motorcycle helmet. Those too can be had in almost any colour and shape. The Vietnamese have a thing about head-wear, and a normal motorbike helmet simply isn't enough.
I shot 1,700 photos during my three days in Hanoi, most of them with the old, non-D 85mm, so I have a lot of sorting to do. Avoiding the tourist traps, Hanoi is really one of the most photogenic cities in the world, even if people in general are a bit "photo-shy".