Last year I was fortunate enough to take two extended self-guided food tours, one to China and Taipei, one through Southeast Asia, with a particularly focus on food in less formal settings — in food courts, at night markets, from streetside counters, from traveling vendors. (You can see pictures, by city, at http://www.flickr.com/photos/eatingin...)
Outside of Singapore, which posts eight-inch-tall lettered grades from A to D, I don't know much about the health inspections for vendors in these countries. When deciding where to eat, I relied on my eyes, my nose, and, when available and intelligible, on word of mouth. I did visit a travel medicine specialist beforehand and described my intentions in detail; in addition to vaccinations for hepatitis B and typhoid, I received a preseciption for an oral antibiotic, just in case something seriously disagreed with me. During eleven weeks of travel, I had occasion to use it just once; my stomach was less seriously upset three other times.
This year I'm traveling mainly by Metrocard and foot throughout Manhattan, the outer boroughs, and enrivons, and I'm still on the prowl (though with much less to show) for street food and the like. Recently I bought an item from a vendor who almost certainly was not fully licensed; later I witnessed that vendor being written up by the police for certain violations. (The details, I don't know; the food was fine, and so was I.)
My question for chowhounds: Whether you're traveling abroad or simply exploring your own neighborhood, how comfortable are you with street food? Would you always want to be assured that the vendor had been vetted by the local health authorities, or are you willing, in part, to judge for yourself?