37 Signals, as usual, has a thoughtful post about self promotion.
Except they missed the biggest part, by a mile.
They don't do self-promotion. Self-promotion, as the term is used by many people, is a mildly pejorative way to describe someone who promotes himself at the expense of others.
Nobody says, "That Yo Yo Ma, he's so self-promotional," or, "can you believe what a self-promoter the Dalai Lama is?" That's because they're not promoting themselves. They're promoting useful ideas. They're promoting tactics or products that actually benefit the person they're reaching out to.
Paris Hilton is a self-promoter. You don't get any benefit out of her appearances other than temporary entertainment value and some schadenfreude. The guys at 37 Signals have never done a bit of self-promotion in their entire careers. That's because they're doing you-promotion, not me-promotion.