Okay, I'll admit it. My med school sends out a syllabus from the biochem department and recommends you kind of read up. I checked out a relatively short, thin biochem for med students book from an academic library and read through it, trying to get a working familiarity with the concepts. I think this gave me a feeling of greater comfort and familiarity for the first block exam (about 3 weeks worth of classes) and the seven to ten hours I spent reading and studying over the summer (plus the five to seven hours I spent procrastinating and/or agonizing over not finishing the whole thing) saved me possibly three hours of study time in that semester. After that first block, the benefits were lost.
If you're a type A personality, full-class worrywart like me, you probably will feel better over the summer if you do something like this. It's probably worth it just for that. Just be aware that the actual benefits during the semester will be quite limited.