I've done the same as Ben for traveling--2 sets of clothing (one on me and one in my pack), every evening spot clean the outer clothing and rinse out socks and undies. If outer clothing needed more than spot cleaning, I'd take it into the shower. I do take pajamas when traveling, though, so the daytime clothing can dry! Every couple of weeks I'd find a laundromat and do a real laundry.
Packing light allows more room for important souvenirs picked up while traveling, such as bottles of wine in la belle France!
For backpacking, only one set of clothing (on me) and use my base layer (normally not worn while hiking) at night.