Here's what little I've learned about disk mounting. Mounting of the filesystem permissions is different than permissions of the files on a vfat filesystem. The permissions are established on the mount point. Without user permission/s, your [e.g., EXT4] filesystem won't be able to read that vfat drive. The following pages on
chown and
chmod explain the options better than I ever could. And don't miss
mounting via fstab as an option.
Most distros like openSUSE, Mint, Mepis, PCLinuxOS, Mandriva, et al. will easily mount vfat USB sticks. I don't run Ubuntu, so I've not run into this problem. Wish I knew more.