A recent PQ Media study reports spending on word-of-mouth marketing in 2006 was nearly $1 billion, up from $76 million in 2001, and is expected to grow to approximately $3.7 billion by 2011. The findings validate word-of-mouth marketing as an industry and should make PR pros take notice.

Evidence of the boom is in the coverage. A search yields 1,786 articles on the subject in the last two years alone. With publishers seeding galleys to book groups, Broadway show ...