"On extended trips (2+ weeks) how do you guys manage your clothes? It seems you'd only want an extra set with the idea of "washing" them along the way (no soap) in a creek or some such. We don't mind getting a little dirty and wearing the same stuff for the weekend, but I'm not so sure about a month, or even a week!"
As Oregon Mouse said, you don't really *need* that much in the way of clothing. A common saying among long distance hikers is that if you can't put all of your clothing on all at the same time (and in coldest conditions want to do so), then you're carrying too much. Too much weight and bulk in clothing is likely the most common issue that makes packs too heavy.
That said, related to the "minimize clothing" mantra is a degree of experience to make that work safely and with acceptable comfort. It's partly about 'style' issues, such as wearing rain clothing while waiting in a laundromat. I personally carry a light pair of shorts and t-shirt that I can wear, putting a puffy jacket over that if cold, and I look a little less like a pervert in the laundromat thereby. The shorts double as spare underwear, so there's little added weight or bulk.
I pretty much never wash clothing in the woods. I find I'm fine for a week or so, never had any health/hygiene issues as a result, but definitely do appreciate the shower and chance to wash clothes when resupplying in towns.
But bottom line, if you're long distance hiking the chances are that you neither have nor want an "extra set" of clothing.