The MacArthur Fellows Program is intended to encourage people of outstanding talent to pursue their own creative, intellectual, and professional inclinations. In keeping with this purpose, the Foundation awards fellowships directly to individuals rather than through institutions. Recipients may be writers, scientists, artists, social scientists, humanists, teachers, entrepreneurs, or those in other fields, with or without institutional affiliations. They may use their fellowship to advance their expertise, engage in bold new work, or, if they wish, to change fields or alter the direction of their careers.
Although nominees are reviewed for their achievements, the fellowship is not a reward for past accomplishment, but rather an investment in a person's originality, insight, and potential. Indeed, the purpose of the MacArthur Fellows Program is to enable recipients to exercise their own creative instincts for the benefit of human society.
The Foundation does not require or expect specific products or reports from MacArthur Fellows, and does not evaluate recipients' creativity during the term of the fellowship. The MacArthur Fellowship is a "no strings attached" award in support of people, not projects. Each fellowship comes with a stipend of $500,000 to the recipient, paid out in equal quarterly installments over five years."
Here's the 2008 list. Check to see if you're on it.