Amazon S3 (Simple Storage Service) is the web service part of Amazon Web Services (AWS) for the cloud storage.
It’s designed both for home and business user, the main features are:
– secure and robust (see encryption)
– reliable, at least 99.9% percentage
– pay only far what you use (see pricing), moreover you can use free for 1 year thanks to AWS Free Usage Tier
– standard or reduced redundancy storage (see the FAQ)
– simple online management with AWS Management Console
– provide tools for developers: REST and SOAP API, SDK for various programming languages and platforms
The mechanism is simple: you create containers called buckets (over 100 for a single account) and inside you can add objects (5tb max for a single object, unlimited number of objects), you can store any kind of data.
Typical usage scenarios are data backup and restore, storage for data analysis, storage static content of web applications, media files (you can use as CDN, content delivery network, eg. see WordPress CMS).
Over the console, there are many clients and tools for various OS (desktop and mobile) that you can use, here you can find a good list.
With these 3rd party programs you can for example share your objects with other users, schedule automatic backups, map S3 as network drive.
I think that a notification system (via web o mail) when you do some action (eg. upload) is an important missing feature.