I usually catch them crawling up my legs. If you don't catch them, they do try to make their way to your neck, under arms, etc. I don't think they actually drop from trees 82nd Airborne style. They cling to brush with their leg out-stretched waiting for something to brush against them. Then the hop on. If you rarely touch brush in the woods, you rarely get ticks. The permethrin manufacturers recommend that you wear long-sleaves, keep your shirt tucked in, and even tuck your pants into your socks. That way they have to touch your treated clothes in order to get to you.
My favorite part of permithrin is that it actually kills the little devils.
Yes, zradix, it's fine to have the treated clothes touch your skin once they have dried.