Anecdotally, I went to undergrad at a school with an elite MBA program. It seemed to me that the only hard part of the MBA program was getting in; the MBA students were essentially paying to have a 2 year networking party. Their experience was like being in college, except they had money to spend and grades didn't matter (due to a grade non-disclosure policy for MBAs).
Because of this grade non-disclosure, the MBA was significantly easier than the undergraduate degree. Many classes had an undergraduate section and a MBA section - the same material taught by the same professor. After the midterm and final, the professor would post the median test score and standard distribution in order to establish the grading curve. The median score for the MBA section was consistently 1.5-2 standard deviations below the undergrad median.
Sometimes a class would be offered to mainly MBAs, but a few undergrads were able to enroll...this was always great for your GPA.