98% of the time I wear steel-toed boots, if I get them hideously dirty or spill something on them that might eat my skin I'll wash them...otherwise...I'm not too picky on how they look.
My wife does //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
She actually scrubs them by hand to get all the loose soil off, then puts them in the dryer on delicate. She puts the hat rack in the dryer and runs them on low or medium for a couple of runs.