squashfs gives a lot of compression, but cannot be modified. cramfs is not so good but allows changes.
if these were included in zubuntu then it'd make life much easier for people wanting to hack about with cacko whilst running zubuntu!
p.s note that newer versions of squashfs-tools can produce file systems that cannot be mounted on older versions. cacko uses older version so you have to use an old version of mksquashfs to generate files, as I found out when making archives of this forum for off-line viewing.