In Atlanta (well, actually I mostly thrift in Roswell), I seem to have more luck with high-end shoes than suits or blazers. Yesterday's HF Boardroom from Saks was the first "good" suit that actually fit. And when I find something good, it's usually one piece at a time. I have no idea how these guys pull trunkloads of high-end clothes.
I've been thrifting since about November.
Yes, I've had ok luck w/ shoes. My local goodwill practically keeps Bostonian and Florsheim oxfords in stock. Haven't run across anything special yet, but they'll do in a pinch.
On how to score truckloads of high-end clothes, it's probably just volume and time management. I only hit one store a day, because I live too far away to spend a lot of time thrifting after work. I'm moving to Virginia Highlands next week, so I'll be able to add more stores to my rotation.