Amazon's uptime is not that great. In fact, Amazon is probably one of the worst run "engineering" companies around. They hire bright people (generally) they just don't make them managers.

Before I left, my manager (after a reorg) was a totally incompetant jerk whose prior training was a degree in "criminal justice". He knew nothing about software development, and had been at amazon his whole career- 7 years managing programmers.

I am amazed that they have only a few days of downtime a year.

I wouldn't be using S3 myself, except that (contrary to advertisements) its not run on the same "proven" infrastructure as their ecommerce platform-- but a new one built by a seperate team, and that team isn't hobbled by the incompetance that has built up over the years on the ecommerce engineering side.