In my experience, there is one additional (and important) risk caused by not having communities: communities change the way your company operates, and those changes are all about BUSINESS AGILITY. This type of change may be more important in the long term than any other tactical change, such as improved customer feedback or brand dilution.

The problem is, those changes are not visible unless you have been on both sides of the issue, and in that case you don't need it

Bu this catch-22 is not hard to circumvent: changes brought about by communities becomes apparent when you attempt to REMOVE such communities from Business Units or Lines of Businesses that are already using them; a typical example will be that of a community falling through the cracks in a business reorganization. Having gone through the process, I can testify that participants feel that letting go on the community is like being asked to work inside a hole in the ground, and will resist the move to the point of quitting and/or mutiny.

Common organic changes produced by self-sustaining communities include:

• Emergence of customer advocacy roles where there were none
  
• Increasing involvement of customers in product cycles, and increasingly earlier in the cycle
  
• Drastic increases in accountability at all levels
  
• SIgnificant reduction on workflow FUD (red tape) by moving decisions downwards in the organization
  
• Much stronger competitive stance; a $1BN revenue vendor I am very familiar with has a cash-cow product that has been turned pretty much obsolete by a platform vendors' free product. Yet, the cash cow continues, the product remains the absolute leader, year after year, and all of it is fueled by its community. Effectively, the company in question remains competitive because of that community.
  

That is probably what the "July 2008 McKinsey Quarterly survey on Web 2.0" talks about when it says that successful adopters of Web 2.0 have found new roles and functions created, and one third of them (the satisfied ones) feel the tools are changing company structure. All of those changes are structural, not tactical.