Expand your file system on the SD-card
From Klaus' wiki
Just after you transferred the image to the SD card it may not quite use the full capasity of the Sd-card.
You can expand the partition by issuing:
] $ sudo /opt/scripts/tools/grow_partition.sh
and reboot to take effect.
Reference
Thanks for the tip to Malthe, who found it over at eliunx.org