Wharton has an interesting article on word of mouth marketing which focuses on whose words are more important. (If you’ve read The Tipping Point, from Malcolm Gladwell, which I’m currently doing again, you’ll say “of course! some people’s words are more important than others”).
Essentially the article says that you can’t assume the “opinion leaders” are the people who say they’re opinion leaders: often if they consider themselves an opinion leader they don’t bother to listen to what others are doing.
In Gladwell’s terms you need mavens: people who love to gather and share information (sometimes called know-it-alls if you don’t agree with them or value their information!).
Who are the mavens in your business? Who’s touting your marvellousness whenever possible? I bet you could find that out by just looking at your own patterns of business!