The Power of Google's Long Tail

TheLongTail offers a supurb summary of what makes Google's business model so intriguing:

What Google has done is to find and monetize the Long Tails of both advertisers and publishers. These include millions of small companies and individuals who may never have advertised before, at least not nationally. They were considered sub-scale--too small to be worth a call or visit from an ad salesperson, possible too small to even think of themselves as an advertiser at all. But Google ads are self-service, cheap, and performance based (pay-per-click), which all combine to dramatically lower the barrier to entry.

Matching these advertisers are hundreds of thousands of previously sub-scale 'publishers', from blogs to niche commercial sites. Most are too small to have their own ad sales business, but they can now run relevant Google ads by just adding a few lines of HTML to their site. About half of Google's business now comes from such 'partners', rather than from ads sold against search results themselves.

eBay works similar wonders.