Getting ready to start riding at least one of my motorbikes in HK, and for summer (unfortunately at the same time!), which has turned up the Veskimo Personal Cooling System. It looks like the backpack version would cost about US$550, shipped, so it's not cheap, but by most reports I've read, it should work very well in our hot and humid weather. OTOH, my commute shouldn't be more than about 35mins--unless there's traffic or something. Hmmm...