i'm in advertising right now for a big global agency. while an MBA is necessary to get to the top, you don't need it to do well in the industry.
my work right now is pretty much post MBA level in advertising agencies...i had an offer on the table last month for a director role if i wanted to stay with the company instead of going to do my MBA next year and i turned it down. to be honest, the quality of people in advertising is weak compared to banks or consulting. i often find myself explaining the simplest of financial concepts to people here. simply put, nobody has any idea of business or P/L unless they are Group Account Director/VP or above.
to me, advertising is almost like a big imbred family sometimes. once you get your foot in the door, you'll be able to move around anywhere in the industry and get good jobs. people are constantly getting promoted and the turn over is crazy. also, just a note of caution, MBA's are not necessarily valued here unless you already have previous industry experience. case in point - we have interns from MBA's (of course not the best programs, but still...) that are starting at the bottom of the ladder along with other interns from community colleges (no joke).
i think our company is actually in the midst of a major overhaul in North America to change senior account management roles to hire more MBA's, because the other ppl we hire can't run a company for squat and really don't bring much value for the 6 figure salaries they collect.