One of the best resources I have found is the "Mentoring for Succession:Countering Aging Work Force Issues" document pubished by Allison McWilliams, of the Carl Vinson Institute of Government, a public service and outreach unit of the University of Georgia.
In this document, the
section on Succession Planning describes some startling statistics

which demonstrate why we need to get better at succession planning.
- 172 corporate vice presidents were in the World Trade Center at time it collapsed.
- 87% of senior managers and 78% of middle managers in the Federal government are eligible to retire
- 1 in 7 number of senior executives in the Fortune 500 are eligible for retirement in the next few years
- Airline pilots, industrial engineers, college professors, and HR practitioners are the occupations with the highest percentage of job incumbents age 50 or over
- Government (at all levels) and light manufacturing industries in the US have the most aged workforces
- Right now, one million college professors and one million public school teachers are eligible for retirement and 50% of all community college presidents are ready for retirement.
- Nationally, half of secondary school teachers are 45 years old or older, with 65% expected to retire by 2008.
- 2/3rds of the increase in the US Population between 2000 and 2050 will consist of immigrants. This means that applicants for these positions will be lacking:
- English proficiency
- Sufficient education and training
- Citizenship
Additionally, every year for the next three decades, there will be fewer young people entering the job market than there are workers leaving.
I suggest you check out the entire document. It isn't short, but is comprehensive and should be "essential reading" for all readers of this space.