I use Permethrin on all my outdoor clothing and some gear. I treat my socks, pants, outer shirt, and hat about once every 6 weeks or so, like the normal spray directions indicate. I treat my hiking shoes (Merrill Moab Ventilators and Palladiums, both cloth uppers) and hammock (and sometimes my pack) once a year, usually just before a long trip in the summer.
The spray stuff is too expensive per use. Someone designed a kit for use by soldiers to treat a uniform, under field conditions (meaning, nothing fancy available to do it with) consisting of a concentrated solution (to be diluted with around 32oz of water), a pair of latex/plastic gloves, and a big plastic bag. I get the concentrate from Tractor Supply and dilute it myself (it comes with instructions for all sorts of uses, from dairies to cow/horse spray), put my stuff in a trash bag for a couple hours, and then hang it on the fence to dry. I figured out the dilution rate for 32 and 48 oz of water; one for just a set of clothes, the other for a larger load that includes gear.
The most useful piece to treat is the hat... ticks usually fall on me from above, crawl all the way across the full brim, and generally die before they get to my neckline and crawl in. that's the theory anyway.