In order to be in both program, the latest u can apply to is the fall of ur first year at pharmacy school. So if u are interested in it I suggest u plan ahead for ur letter of recommendations and GMAT. If you are pharmacy student, they wave the 2 year work requirement and being in one USC program gives u a slight advantage of getting into the other program I think. (Even though they say they don't!) However, u will have to apply to both programs seperately and be looked over by two different admission committee.
I think there are several reasons why I think the pharmD/mba program is not that popular. First, the deadline for applying for it is too fast. Most pharmacy students are so busy trying to get use to pharmacy school and the work pace that they simply have no time to apply. Since the latest u can apply to it is fall of first year, many students are not able to have everything in time, gmat scores, recommendations and etc. unless they plan well ahead. In addition, the program is very selective. The two students who were offer acceptance into the dual program during my year are some of the smartest people I have seen and are top students in my class. In addition, most of the students in the pharmacy school are into science and healthcare. During pharmacy school at usc, there is a management class that every student has to take, which I am sorry to say, that the majority of the students did not like. Simply put it, the majority of the students are not into econ or managment or accounting. Finally, it does take more time, effort, and money. So unless u have a clear vision of what u want to do with that extra degree outside of having more letters behind ur name, it would be a waiste of time for most to apply. Some of the fields that pharmD/mba might go into are marketing and administrative practice such as management.