Thanks, Vintage Gent. No doubt to my wife's ever-lasting chagrin, when I visit a new place one of the very first things I want to do is scout out the thrifts. Looking at what people have discarded can really give you a feel for a place. And you never know what you might score. Hope springs eternal for a stop at one of those places where age, income, and a suitably laissez-faire approach on the part of the thrifts all come together to create a gold mine. I know they're still out there.
Your mention of the SA raises a good point. Specific charitable organizations (Junior League, Symphony, hospitals, schools, etc) often have, on the whole, nicer goods. For the casual thrifter, they're also easier to deal with since the selection tends to be limited and well-displayed. But some of my best finds have come from big grungy warehouses--like some of the SAs--where everything's simply sorted by color and put out on the floor by people who have no idea what they're dealing with. On most days, I'd have no trouble opting for a go at a couple of big unsorted bins at the GW over a polite look at some of the fine offerings at the American Cancer Society. Volume is your friend!