This so wierd. I'm also leaving for vacation and this happened to me twice last night. gtkpod froze during the middle of transfering music (I suspect it might be the hfsplus module) and I could not gracefully kill it, so did a eject /dev/sda. When I tried to mount it dmesg said the same old stuff about the filesystem being read-only so I took my own advice with hpmount /dev/sda and hpumount and I also corrupted my files....that's why I'm a n00b I guess! According to
http://www.ipodlinux.org/Installatio..._Linux_Hfsplus, under "The Annoying Bug" heading, it seems you have to run this command when ipod is plugged in but not mounted. Mine must have been mounted because I've run these commands before and ipod was fine. Anyways, what you have to do is use a mac (if you still want to use the hfsplus filesystem) or windows box and go to
http://www.apple.com/ipod/download/ to retore the firmware (you might also be able to do this with the cd that came with your ipod) I don't know about windows but on a mac this only takes a few minutes. This reformats the ipod, so you will need to put all of your music back on. Also, the ipodlinux.org article mentions how to back up the ipod to a (big) disk image so if your ipod's filesystem does become corrupted again, you can retore it without having to find a windoze or mac machine.