The lesson of using the development branch of a Linux distro

Is that it may crash and unequivocally prevent you from ever being able to log on to your system ever again. :(

I had Ubuntu Hardy Heron for a couple of weeks already. After upgrading with tonight's updates, on libc6 and various other critical-looking packages, the upgrader crashed, and now, I can't even boot into my system, no matter what kernel I use. These bugs on Launchpad (201688 | 201694) were filed just a few minutes ago, about the same problem that I experienced (thankfully, in real life, you have Windows). We hope that there are still brilliant techniques to save a system that is now un-usuable, even in recovery mode.

Edit: It was indeed glibc... (Launchpad: 201673) Looks like the solution is boot from a Live CD, and fix the system from there.