From my experience at Michigan (Ross '06) much of the advice above applies for an MBA, but there are some significant differences. First, networking matters even more at a top MBA program. We used to joke that b-school is a $100K job placement service, and if you want, you can skate through as no one washes out of b-school. At many schools (including Ross) you won't even know your class ranking, as the idea is to reduce destructive competition and prepare students for a teamwork focused business career. You have to work the alumni and club network from day one, particularly when aiming for banking, management consulting, and consumer goods jobs. First year Ggrades still matter for these traditional MBA channels, but much less than Law, it seems, and school reputation matters even more for the big jobs. You will not see McKinsey or Goldman Sachs at MSU or OSU, and many won't consider part-timers.
If considering an MBA, I would recommend following a traditional track to IB, consulting, or CPG, even if you don't plan on making a long term career of it. Having a "name" on your resume will open doors for the rest of your career, no matter what you decide to do. Any corporate frecruiter will respect a few years on wall street, or at Procter & Gamble, or BCG. Plus, you will probably learn more in a year than you do in 2 at b-school.