Medical schools evaluate the difficulty of your curriculum after the initial screening process. If you have taken fewer units per semester, your GPA will be seen as weaker than someone who took more units each semester and recieved the same GPA. However, if you are taking a normal number of units each semester then you should be fine.
I'm glad someone posted a thread about this. I've been contemplating (sp?) doing the same thing. This would give me more time to get a minor or two, and an extra year for some extra curriculars. But the downside is the money, I go to a private school and that $hit costs some major dough. Just puttin in my 2 cents.