In HBR this month is a rare, methodical (and free) look at the financial effect of online communities via a study of eBay Germany…

Over the course of a year, we compared the behavior of community enthusiasts and lurkers with that of the control group. The differences were astonishing. Lurkers and community enthusiasts bid twice as often as members of the control group, won up to 25% more auctions, paid final prices that were as much as 24% higher, and spent up to 54% more money (in total). Enthusiasts listed up to four times as many items on eBay and earned up to six times as much in monthly sales revenues as the control users. The findings on first-time sellers were even more impressive: Compared with the controls, almost ten times as many lurkers (56.1%) and enthusiasts (54.1%) started selling on eBay after they joined and participated in customer communities.

The challenge for companies now is remembering that creating community means getting like-minded groups of people together to do things they like doing and not just installing some community software.