Interesting article on Trader Joe's from Fortune:

A closer look at its selection of items underscores the brilliance of Coulombe's limited-selection, high-turnover model. Take peanut butter. Trader Joe's sells 10 varieties. That might sound like a lot, but most supermarkets sell about 40 SKUs. For simplicity's sake, say both a typical supermarket and a Trader Joe's sell 40 jars a week. Trader Joe's would sell an average of four of each type, while the supermarket might sell only one. With the greater turnover on a smaller number of items, Trader Joe's can buy large quantities and secure deep discounts. And it makes the whole business -- from stocking shelves to checking out customers -- much simpler.

In a lot of ways, Trader Joe's has more in common with Wal-Mart than with Whole Foods or a farmer's market.