There is an interesting thing I have recently learnt:
GMAC is not the one who creates tests or runs them. Actually, ETS (Educational Testing Service) comes up with test questions, methodologies, scoring, distributing, etc. They are contracted out to do the job. In contrast GMAC oversees the whole procedure, collects statistics and maintains a liason with Business Schools.
ETS, in fact, runs many tests, around 200 I believe. Whereas, GMAC is in charge of only GMAT. 3 years ago, GMAC had less than 10 people on staff.
This definitely goes agains the stereotype.