I've heard it called "The Bins", "As-is Goodwill", or "Last Chance Goodwill", but whatever you want to call it, it is my favorite thrift store in Portland. Everything is wheeled out in big blue bins throughout the day and it is up to you to dig through the items to find treasures. The only sort of organization that exists is that the bins are loosely sorted according to contents such as shoes, books, electronics, textiles, glassware.
The warehouse space is huge and it can be a bit overwhelming the first time you go. There are people who shop there regularly that obviously take it very seriously. If you are a first timer, it is best to stand back and learn from the regulars.
The majority of the items are sold by the pound. The more you get, the less you pay per pound. If you walk away with 50 pound or more you are going to pay the lowest price per pound. (Something like $0.89 a pound.) Some of the larger items like furniture are marked with a price and books and glassware have their own prices. I believe it is $1 for softbound books and $2 for hardbound.
Your best bet is to go with specific items in mind, but be open to possibilities. You never know what you are going to find!