ChAoTiCpInOy, S3 is fairly expensive in my opinion, has basically no guarantees/warranties of anything, my personal experience of Amazon's customer service is very negative, and other people's experiences of S3 and their cloud services are mixed at best (reliability and customer service, I hear a lot more negative than positive, but a lot of people like the concept). Also, I've seen their facilities and I know how the sausage is made, so, well, that made a strong impression too about whether I'd want them anywhere near my data.
The idea of combining redundant not-quite-reliable hosting providers might not be a bad idea, depending on your requirements.