OK, if you have fanoush's initfs setup (I did, but hadn't yet cloned the OS to the MMC card), you can download the dev firmware tarball from here, untar it to the proper partition of an MMC card (whatever your device is set to boot from), and boot from that. This is a stripped-down OS, with basically only an X-term to work with, but that's enough to mount the internal filesystem, and copy everything off. Of course, it would be better still if I'd set up the dual-boot promptly in the first place!

I haven't experimented much, but you may be able to set up a chroot environment and uninstall whatever it was that caused the problem via dpkg.

I will definitely be keeping an MMC card handy with this rootfs on it for emergencies!

P.S. If you haven't yet setup fanoush's initfs, there may still be a way to accomplish this, by setting up the card, then using the flasher tool to boot from an MMC card. I haven't experimented with this, see this page for details

EDIT: chrooting does work, but I wasn't able to pull off the offending package, as I'm not sure which package it was, so I re-flashed.