While I can't appologize for trying to talk someone out of riding in a kilt, Sushi is right, I should have at least tried to answer Seaborn's question. I think he can pretty much wear whatever kind of kilt he wants. For those who don't ride, let me explain. The seating position on a Sportster like SeaBorn's is pretty much like sitting at your dining room table, unless it's the "Custom" model where you sit lower, with your feet farther out in front of you. Hurricane force winds start at around 73 miles per hour. So next time a hurricane comes through, take a dining room chair out into the street, face it into the wind, and sit in it.That's what riding at 70 mph feels like. Leather isn't going to stay put any better than a lighter material. That's why the riders in the preveous thread talked about using a 16 oz magnet to pin their kilts to their gas tanks.
I haven't got a PV kilt yet, but I assume PV and leather would be the easiest to clean. Before I became an old safety nazi, I used to occationally ride in baggy shorts, and it was my experience that leaking oil and road debris like rocks, etc would usually hit below the knee. Lighter debris, like big cream filled bugs, bees, wasps etc would either hit below the knee, or be blown up the shorts leg. I assume a kilt would work the same way, so it will actually stay cleaner than you think. Again, pretty much whatever kind you want to wear would work jsut as well.

I hope that helps,
Java