I use S3 a ton. I have over 40 or so buckets floating around between clients. I like the fact that I can list them in /etc/fstab and that they just work. For reference here is one of the buckets.

coteyrnet /mnt/S3/coteyrnet fuse.s3fs _netdev,use_cache=/tmp,use_rrs=1,allow_other,noauto,users 0 0

It mounts fine, but I am having one heck of a time unmounting it.

The first problem is:

umount: /mnt/S3/coteyrnet mount disagrees with the fstab

The relevant part of mtab is:

s3fs /mnt/S3/coteyrnet fuse.s3fs rw,noexec,nosuid,nodev,allow_other,user=coteyr 0 0

In addition to that, if I sudo umount /mnt/S3/coteyrnet I always get

umount: /mnt/S3/coteyrnet: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))

lsof | grep coteyrnet never returns anything of value, nor does fuser.

My goal is to get user unmounting working.

The inability to mount via sudo has been resolved. By using the "use_cache" setting the files were actually open, but not under the mount point. This is a caveat to that option. The mount point files are closed but the files were not yet transferred to S3. By waiting "a while" and trying again, sudo can unmount.