Better known as the df plugin. This adds an item to your Audio, Video, Games, and Pictures Items. It states how much memory is free on the partition that directory belongs to.
To activate it, put this in your local_conf.py:
To see the disk usage go to any directory listing and, press ENTER ('e' key or key it maps to on your remote) and you will see the disk usage under the Browse directory option. This also works on the main directory listings where you see your cdrom drives.