My friend asked me to save his data on a Mac OS X partition since his machine couldn't boot properly into Mac OS X GUI mode. So I booted the machine with Ubuntu 5.04 Live CD. I know it was an old version but who cares as long as it supports hfsplus filesystem used by Mac OS X.
So I mounted one of the partitions where he saved his work with this:
sudo mount -t hfsplus /dev/hda5 /mnt (for Ubuntu)
(If you are using other distro and logged in as root, just omit the sudo from above command.)
where /dev/hda5 is the partition and /mnt is the mount point.
From now, insert usb drive and copy file to it. After this, he can wipe out all partitions and/or reinstall Mac OS X.