After more thinking about the way it should work, I have some more details.
Once a removable media is inserted (but not explicitly mounted), there should be an icon in the notification area with a symbol representing such media or a plug of some sort. The icon should have a check-mark to show that it is safe to remove. When an application writes to the fuse filesystem, it is actually written to a temporary place on the hard disk; at the same time, a daemon sees that something is being written, turns the notification icon to an x, re-mounts the removable media as read-write, and starts writing. Once it's done, the daemon re-mounts the drive as read-only, deletes the temporary data, and turns the icon back to a check-mark.
If the user does happen to remove the drive while it is being written, a notification pops up that says there is still data waiting to be written to the disk. The daemon records metadata for the removable drive (possibly its GUID) so that it can finish writing it the next time it's plugged in (or notify the user and ask the user to view and possibly re-save files if it has been a while or the drive contents changed since).
After more thinking about the way it should work, I have some more details.
Once a removable media is inserted (but not explicitly mounted), there should be an icon in the notification area with a symbol representing such media or a plug of some sort. The icon should have a check-mark to show that it is safe to remove. When an application writes to the fuse filesystem, it is actually written to a temporary place on the hard disk; at the same time, a daemon sees that something is being written, turns the notification icon to an x, re-mounts the removable media as read-write, and starts writing. Once it's done, the daemon re-mounts the drive as read-only, deletes the temporary data, and turns the icon back to a check-mark.
If the user does happen to remove the drive while it is being written, a notification pops up that says there is still data waiting to be written to the disk. The daemon records metadata for the removable drive (possibly its GUID) so that it can finish writing it the next time it's plugged in (or notify the user and ask the user to view and possibly re-save files if it has been a while or the drive contents changed since).