Just to close the loop on this... I had an old Giro Vapor 3, I think, from when I first got my bike years back. Started riding with that just as the heat kicked in. Made me realize two things. One - it felt like wearing... well a helmet. While there were vents in it, it certainly didn't *feel* like there were vents - no wind, no cooling, so I got to work even hotter than usual. Two, I really like biking w/out a helmet - the sense of motion around my face is really one of the things I loved.

So to make a long story slightly less long - after doing much research and seeing the Specialized Propero II and the Scott Vanish R, I kind of thought those were what I'd like. Went to my LBS and walked out with a Giro Pneumo - which in many ways was what I hoped to avoid before I realized that the point of the helmet was protection and second most important to me was ventilation. Style dropped to a very distant 3rd. Been riding with it for a week or so now and glad I got it sooner rather than later. Biking is much more enjoyable w/ it than the Vapor. Thanks for everyone's advice here!