I can't ride without either goggles or a helmet with a face shield - I can't keep my eyes open in the wind (and I've tried shades and motorcycle glasses, they don't fit my head shape well enough). Other than that I always wear a helmet for anything going past the stop sign at the end of the street. If I'm going on a "ride" then I wear boots, jeans, and a mesh riding jacket. Going to work takes 5 minutes with a 40mph top speed, and I have to wear slacks and a button shirt once I get there. I wear the jacket if it's cold, otherwise I just wear the helmet and my work clothes.
I would do the same on any style bike (currently have a Versys as primary street ride). If I was more comfortable without a helmet I MIGHT go without from time to time, but probably not - too many head impacts on dirt bikes for me (usually tree limbs, which shouldn't happen on the street, but it's a habit).