Included in this overview is a 2005 salary survey (PDF).

"Over a third of the members surveyed in 2000 had degrees in HCI (Human-Computer Interaction) or Human Factors, Psychology or Computer Science. Other educational backgrounds include Business Administration or Management, Experimental Psychology, Technical Communications, Fine Arts and other Social Sciences."

http://www.usabilityprofessionals.org/usability_resources/about_usability/about_usability_professionals.html