Yes, OB is very different from med/surg. Obviously, each nursing student's clinical rotation experience differs, depending on the student, the clinical instructor, the clinical site, the nurses on the unit, the patients, etc. etc. In my personal OB clinical experience as a nursing student, we were fairly limited in what we were allowed to do.
I passed meds maybe a handful of times (mostly IV antibiotics in labor and PO pain meds in postpartum). I observed vaginal and C/S deliveries and epidural placements. I bathed a newborn. I inserted a couple foley catheters and started an IV. I did a few assessments on moms and babies, although they were not full assessments, and were a bit limited. I was one of the few in my clinical group who was allowed to check a laboring patient's cervix. Expect to spend a lot of time observing (and staying out of the way). Also expect the possibility of patients turning down having student nurses participate in their care (this tends to happen a lot with the male nursing students). In labor I often had a lot of downtime, waiting for the moms to progress. You'll get some exposure to the OR and Recovery (comparable to PACU) with C/S's. Some parents are very wary of nursing students doing ANYTHING with their newborns or getting anywhere near mom's fundus. Other parents are amazing and will take pleasure in including you in this most intimate of family experiences.
Even if OB doesn't interest you, take advantage of the opportunities you will likely have to brush up on your nursing skills such as starting IVs, inserting foley catheters, and hanging IV meds.
Remember, your clinical experience is what YOU make it! Good luck!