LinkedIn is a 21st Century job board. Although the recruiting vanguard dismisses it for problems with data quality and price to value ratio, the service facilitates individual network development and productivity. Most of the individual users I know rely on LinkedIn for insight into the next person on their calendar. Compared to other job boards, LinkedIn is focused on the expansion of the networks of its members.
The single largest limitation to growth for LinkedIn is the inability to monetize the real value it delivers. LinkedIn preps knowledge workers for the next meeting.
