I haven't used it internally, but I have used cider vinegar topically, with great success.
My daughter has been troubled with a cluster (about 5) of veruccas for years and after reading somewhere about CV being useful for treating warts and veruccas I suggested she try it. She'd tried just about every proprietary remedy in the past with no success, so she was prepared to try anything. However, after several months of religiously putting it on her veruccas every evening and then covering them overnight with a plaster or tape they are all almost gone.
I also decided to experiment with my husband's toenail which has had an unsightly fungal patch on it for many years. I've faithfully applied CV to the nail every night before he goes to bed, making sure it's dry before he puts anything near it, and amazingly it is very slowly clearing up. He was very sceptical about it when I started, but even he says he can see it's getting better now. I really wish I'd taken a before photo as the difference is so obvious. It'll probably taken another 3-4 months before the whole patch grows out, but it's pretty impressive when he's had it for 15+ years!