Another challenge is directory flattening. On a file system "a/b" and "a//b" are usually considered the same path. But on S3 the slash isn't a directory separator, so the paths are distinct. You need to be extra careful when building paths not to include double slashes.

Many tools end up handling this by showing a folder named "a" containing a folder named "" (empty string). This confuses users quite a bit. It's more than the inodes, it's how the tooling handles the abstraction.