By the by, does anyone know where the mount point directory is located?
It depends on how a partition is mounted. If it's mounted by HAL (e.g. automatically when clicking the partition in Dolphin) it would be a subdirectory of /media. If it's mounted at boot it will be mounted wherever its line in the file /etc/fstab specifies -- i.e. wherever you've told the system to mount it. (Subdirectories of /mnt would be good places for temporary mounts.)
Note that a mountpoint is just a directory. Normally it would be empty until you mount a partition on it. If it isn't empty its contents will become unaccessible when the partition is
mounted -- hidden behind whatever is on the mounted partition.
JohnBoy's theory was that you just might have moved your files to a directory where your USB drive (or actually partition) would normally
be mounted. But if it wasn't
mounted when you moved the files, the files would seem to disappear immediately when it actually was
mounted. They would still be on your hard drive though, and reappear if you unmount the USB partition.