There seems to be two classes of hikers, those who wash up regularly (and probably wash their clothes), and those who do neither.
Personally I'm in the former category, and I must admit I do not like meeting up with people in the latter category, especially in hot weather at the end of the day. I've had some pretty unhappy experiences in AT shelters olfactory-wise, and it is not uncommon for people to move out when a particularly ripe person or group arrives.
Warning...about to start a flame war:
Why is washing up once in a while such a big deal? It's easy and takes little time. The old proverb states "Cleanliness is next to godliness". I'm not talking about being squeaky-clean all the time, just an occasional wash-up, depending on temperature, activity level, etc.
Practical point: as you get older your skin may become more sensitive to dirt, oils, salt, etc. These days I get rashes if I don't wash up with some regularity.
Ok, now you can rip in to me for asking everyone to wash up once in a while...