Accessing shared folders in VirtualBox (Linux guest)

Transferring files from the host to the guest OS and vice-versa doesn't work out-of-the-box when you install VirtualBox from the Ubuntu repositories and download an Ubuntu VirtualBox image (e.g. from http://www.osboxes.org/virtualbox-images). After installing the guest additions, drag-and-drop didn't seem to work for me and I needed to set up a "Shared Folder". After setting it up via the GUI, it doesn't automatically appear on the guest desktop. You need to mount it:

sudo mount -t vboxsf name(as_specified_via_VirtualBox_GUI) ~/mount_point_in_the_guest_OS/

There are obviously many other ways how to achieve this (e.g. via Samba or sftp or sshfs)...