I haven't. I'm sort of aware of it but I guess I prefer to just have tight control over the protocol/ data layout. It's not that hard and it gives me a ton of room to make niche optimizations. I doubt I'd get the same performance if I used it, but I could be wrong. Usually the more you can push your use case into the protocol the better.
Like most managed services it is a trade off of control vs ease of operation. And like everything with S3 it scales to absurd levels with 10,000 tables per table bucket