There is some controversy about how much carb is consumed by the yogurt cultures. If you don't have much leeway in your carb counts, it can take a big chunk.
I've had the full fat, no sugar yogurt a couple times a week, it's great with berries, and I haven't noticed it hurting me any. But then I'm at a 40 carb a day level, so it doesn't take as big a bite out of my daily total.