The 8th Annual 2009 Source of Hire Study from CareerXRoads confirms that for those hires originating from external sources; referrals from current or previous employees, customers, and vendors are the number one external source accounting for 27.3% of successful placements.
Nearly 40% of all positions filled within companies result from internal transfers or promotions. Interestingly, job boards (excluding company sites) produce only 12.3% of external hires and seem to have reached their peak.
The report is a concise analysis of the current status of the industry and has insightful observations about the future of sourcing, recruiting, and hiring. A recommended read for anyone involved in the sourcing and candidate placement fields.