Just an hour ago or so I tried to set up a backup to my NAS for some of my folders. I found the tool FireSync and its description sounded promising. I tried to find some reviews but since it has been published just today. So I gave it a shot.
I should have been more careful and try out the backup in a dummy folder, not my main application collection. During the first run of the backup there was an error that "Disk is full" at the backup source. As if that's not strange enough a retry just found 4 or so changed files. Hm... After some moments I checked back the source folders. The folders were still present, but not the files which were contained within them. WTF? I made sure I didn't check the "delete after sync" checkbox and it wasn't. Nevertheless, the files were gone.
Currently I'm busy with recovering the deleted files with NTFS Undelete. So far everything looks good and it seems that I can restore all of my files.
So, if you ever want to try out the backup/sync tool FireSync, test it out in a dummy directory.