Another pharmacist/physician joining in. I worked for a year as a pharmacist before going back to med school. There were three PharmD's in my class. All of us worked per diem throughout first and second year. I continued to work until MS4 because I was lucky I got a gig at the campus student health clinic. Average working 5-10 hours/week throughout. Not bad money at all for a student. Being a pharmacist helped a during pharmacology class but only a little bit. Those med students are smart people, they still beat us on the grade, say I got a 90%, someone else got 100% (and not one of the other two pharmacists in class). During Step 1, I got a lot of pharmacology questions that I was very grateful for. Other than that, everything is new, new concepts to learn on how to diagnose, pathophysiology, pathology etc. Now in residency the only advantage is that I can do discharge order for outpatient without looking up the dosage. But all of my fellow interns learn dosings and such very quickly too.
Bottom line, going back to med school was a great adventure and I enjoyed it very much. Residency is a different game however.