From "The End of Business Schools?: Less Success Than Meets the Eye" by Jeffrey Pfeffer (Stanford University) and Christina T. Fong (University of Washington):
"Although business school enrollments have soared and business education has become big business, surprisingly little evaluation of the impact of business schools on either their graduates or the profession of management exists. What data there are suggest that business schools are not very effective: Neither possessing an MBA degree nor grades earned in courses correlate with career success, results that question the effectiveness of schools in preparing their students. And, there is little evidence that business school research is influential on management practice, calling into question the professional relevance of management scholarship."
Far better to skip the MBA and teach yourself. Better results, and far less debt.