Biz school. Wanna go? You gotta take this test.
It's more or less the SAT, with a few more $5 words and strange computational logic exercises. If you want to sound cool when you refer to it, you'll say "Gee, Matt" and people will think that you've already 800'ed it. And yes, the scoring system is just like the SAT, with thousands of people getting 800s on the exam each year.
So...just getting a perfect GMAT does very little for getting you into Harvard or Stanford. But at least it's a start.