I was on depakote for some months about four years ago and had two noticeable side effects: weight gain and a little sluggishness. The weight gain was annoying, I put about 20 pounds on a 200 pound frame and it didn't seem to respond to exercise. The sluggishness was pretty minor, as I just didn't seem to have the usual energy (usually in the evenings) and only when I was on my highest doses.
If memory serves, I was on a pretty high dosage, 1500 or 2000 mg. I believe the dosage is determined by patient weight.