The report is apparently not online, though you can give them your email address here: http://www.ncwit.org/resources.thefacts.html [Edit: actually it is, just click "no thanks"] There's another article here: http://www.readwriteweb.com/enterprise/2010/06/ncwit-report-... "The NCWIT report contends that 56% of women in technology companies leave their organizations at the mid-level point (10-20 years) in their career…
EDIT: Here's the pertinent section. They are saying they leave the field, not company, mid-career:
"In 2003, only one-third of women with a computer science bachelor’s degree were still employed in a science, engineering, or technical (SET) job two years after graduation. According to a study by the Center for Work-Life Policy, 74 percent of women in technology report “loving their work,” yet these women leave their careers at a staggering rate: 56 percent of technical women leave at the “mid-level” point just when the loss of their talent is most costly to companies. This is more than double the quit rate for men. It is also higher than the quit rate for women in science and engineering."