Just noticed that when you upgrade the plugin to newer version, all the images you've uploaded through the interface get erased... because they are stored by default (and no way of changing it) in s3slider-plugin/files folder, inside the plugins folder.
So once WP replaces that folder with the updated version it wipes out all the files with it too!
Luckily, I had a backup of them... or I would've been royally pissed. But I'm sure a lot of other users won't be happy when they find out the harsh truth that will come out of this small overlook on the coder's part.
I'd suggest fixing that ASAP and having the "files" directory outside of the plugin's folder.