For keeping you safe, I don't think there's much of a difference. What you're paying for, as has been mentioned countless times at this point, is perceived style and the possibility of added comfort (less weight, more vents...) Of course, the more expensive helmet does not always mean greater style or comfort for any given individual. Some may find that the cheaper helmets are more comfortable and more stylish. I think they're wrong, but they're out there I'm sure

That said, I have one of the lower end giro helmets... encinal I think it's called. I think it might actually be a mtb helmet, I'm not sure. I only saw them at the lbs that one time, and I picked it up... Far better, IMO, than the walmart schwinn helmet I had previous to that, in terms of style and comfort, but they served the same purpose as far as I'm concerned. I've been happy with my helmet thus far, although I am considering getting a 'more roadie' type helmet... possibly a bell sweep r, or something like that. Purely aesthetic purposes; I like the way they look.

Watching the TDF in recent weeks has gotten me thinking about this even more, as I think most of the pro's helmets look slick... Which brings me to something that caught my attention last night. On OLN, there was a brief interview with Levi Leipheimer. The very first thing I noticed was that his helmet looked GARGANTUAN! I couldn't tell what helmet it was, but it looked rediculously big. Does the Gerolsteiner team just use larger than normal helmets, or does Levi have a particularly small noggin?