The Conference Board of the Mathematical Sciences, Computing Research Association, American Institute of Physics, and the National Science Foundation collect statistics on degrees granted and faculty demographics. All of their figures indicate that women are considerably less rare among tenure-track STEM faculty than suggested by the figures given in The Mathematics of Sex.
According to the NSF statistics below* from the Survey of Doctorate Recipients,[i] at four-year institutions, the percentages of women in tenure-track positions range from 19.1% (engineering) and 22.6% (computer science), to 29.4% (mathematics and statistics) and 33.7% (biological and related sciences), to 70.4% (health). According to the CBMS 2005 Survey, women are 50% of the full-time permanent mathematics faculty at two-year colleges.[ii]
*Update: The graphic below is no longer visible (at least on my browser), however, it occurs as part of my Journal of Humanistic Mathematics article which can be downloaded here.
[i] National Science Foundation, Division of Science Resources Statistics. 2009, Characteristics of Doctoral Scientists and Engineers in the United States: 2006. Detailed Statistical Tables NSF 09-317. Arlington, VA.
[ii] CBMS Survey, Fall 2005, p. 169.