Thunderstruck- they don't mean open helmets like the old school type- they mean the moto-cross style. So no shield, but goggles instead. These helmets still have a full 'face' and your chin/face area is protected. But rather than a standard flip up shield, the helmet is just open in the eye area and you wear goggles.
I am still considering this switch. I almost did it last year and wimped out. I had another cold season with my modular2 this year. If you don't have the sunshield down, there is a wicked airflow into that thing. When it's -15 out, it's brutally cold. I also have pretty much no windshield on my sled (but it looks cool, so we keep it right? =) I got caught in a pretty decent snowstorm and the lack of windshield, combined with the gap in the helmet was a disaster. I had more snow IN my helmet, than ON it. I couldn't see. It was horrible. So I'll be scoping out/trying on helmet/goggle combinations at the shows this year.