SearchEngineWatch writes about the potential in the SME market:
The answer, as one might expect, is revenue-or more precisely, potential revenue. When you add up the number of all the paid search advertisers in the world right now, the total is approximately 380,000. Yet, there is substantial overlap among the advertisers of the different paid search networks. (It’s rare a company that uses Google but not Overture and vice versa.) So, as a rough estimate, the figure is probably closer to 250,000 paid search advertisers on a global basis.
By contrast, the U.S. alone has about 10 million small- and medium-sized enterprises (SMEs), and there may be as many as 30 million more such businesses in developed countries around the world. In the U.S., most of those SMEs, the bulk of which have fewer than nine employees, conduct the majority of their business within 50 miles of their locations.
The model to look forward to is Citysearch which marries search and directory. “Citysearch presents a hybrid approach that combines pay-per-click advertising for local businesses, with a keyword search-driven interface over a structured local database. That provides the ease of use of search with the reliable structured data offered by Yellow Pages.”