Therese F. Triumph and Penny M. Beile have published "The Trending Academic Library Job Market: An Analysis of Library Position Announcements from 2011 with Comparisons to 1996 and 1988" in College & Research Libraries.
Here's an excerpt:
The primary objective of the study was to describe the number, types and titles, requested qualifications and skills, salary information, and locations of positions advertised in 2011 on the ALA JobLIST and ARL Job Announcements websites and in the print version of the Chronicle of Higher Education for purposes of determining the current state of the academic library job market in the United States. To investigate changes in the academic library job market and identify emerging trends over a 23-year period, results also were compared to studies that analyzed position announcements from 1996 and 1988.