As usual, Seth Godin has a great post: Why Word of Mouth Doesn't Happen. He lists 9 reasons. The first is fairly descriptive. And at the end he adds this:
First, understand that people talk about you (or not talk about you) because of how it makes them feel, not how it makes you feel.
Changing their day, changing their perspective, changing their attitude, changing the way they look at their world is how you generate word-of-mouth.
Seth suggests changing the game:
What will change the game is actually changing the game.
That's a Google or a Twitter-like game changing experience.
Sometimes, it's the simple things that can generate that feeling. Flowers to a new customer or to a customer for their referral worked at my previous company. Simple, inexpensive, personal. WOW. So were our mission to answer the customers' calls in person. My office extension was in that loop.
Granted those things were done delivering a commoditized service. It worked; we grew successfully.
Had we done that with a game-changing service ala Google/Twitter, etc, we'd have conquered the world.
All in good time...All in good time.