I wash mine everytime, in the machine with my usual biodegradable natural non-irritationg CHEAP Trader Joe's laundry soap and usually with other clothes, too. I let them airdry overnight. Even my $19 Nashbar shorts have survived that treatment. They're almost 9 years old now, and just starting to fall apart enough that I'll only wear them as "liners". I have 3 pairs of shorts that I rotate through, so there is always a dry clean pair when I need them. (all different brands) I plan to get a pair of Ibex knickers next, and they will get the same treatment, too.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson