I know a few ABC MBAs (financial and consulting field), under gradulate is from top schools (Columnbia, U Penn, Harvard...). Since they are ABCs, excellent English, very smart. But..... they can not find jobs after their MBA from U Penn (Wharton), Northwest!
The reason I think is because in financial field the best doesn't do a MBA. They move up directly from their jobs. Only the ones not as good need to get a MBA after 2-3 years as they couldn't get a promotion.
So the top Wall Street firms don't want to rehire these 2nd tier people. In this case, having a MBA actually hurts your job prospects.