It has been a long time since underpaid college professors wore tweed jackets with patched elbows. Current compensation would suggest something more along the lines of Armani. [Also see here, and here.]
No wonder then that college administrators, under pressure to contain tuition inflation are shifting away from the tenure-track model, and more and more in the direction of competitively-priced contingent professors.
Contract professors, or adjunct professors, often teach as many courses as their full-time counterparts; however they cannot earn tenure. As of 2003 (the latest data available), 85% of full-time faculty made $40,000 or more, compared to only 4% of part-time faculty.
As can be seen in the chart below, 2011 is looking like it will be the first year in which "part-time faculty" outnumber full-time faculty in United States postsecondary education.