I suspect that the overall uptime numbers for Amazon's S3 service are still very high, but outages like yesterday's really hit people - this is from the FaceStats service, which relies on S3:

It wasn't just us -- dozens or hundreds of useful websites were down today. SmugMug, the photosharing site, was broken. Avatars didn't show up in Twitter. Drop.io, the excellent service we use to send and receive data from clients, was completely down. Scribd had no document data, rendering the site basically worthless. We decided to make the best of it and replace the homepage with an embedded flash game -- since every feature of our site is broken, why not give our users something else to do?

A seven hour outage is bound to get comments - Amazon is going to have to be very open about these problems going forward.