Brand Allegiance

Why do people have allegiances to brands? How are these loyalties cultivated, developed, and maintained? Is allegiance to anti-brands, like American Apparel and the Black Spot shoe, the same as allegiance to branded products? I still need to read No Logo (it's on our bookshelf) and should look at Adbusters and brand forums like mynudies.com. Consumer organized web forums on brands and products are fascinating, here is a quote from the front page of mynudies:

What is Nudie Jeans?
Nudie is the "naked truth about denim". Indigo is the living color that fades and together with your lifestyle gives denim its character. The longer they live the more character they get. Besides leather, only denim has the ability to age so beautifully - formed by its user into a second skin. Jeans are a lot more than just a piece of clothing; a pair of jeans is like a second skin, naked and personal = Nudie.