Where are all the good end-user tools for S3 now?
As others have mentioned, Dropbox and SugarSync are consumer interfaces to S3. I think the fact that Amazon references "objects" and "buckets" in S3 terminology is directly because they didn't really build S3 to be an "online file system" type service (though s3fuse provides it). They intended to be merely the backend for the consumer services you mentioned.
That being said, clients aren't always strictly downloadable software. My most-used S3 client is built into my Synology DiskStation NAS and provides nightly backups to S3 (hopefully they add support for Glacier). Also, I frequently use Panic Transmit for Mac OS X, which is an FTP client that also has support for S3.