Yes, I've seen some remarks saying that you can basically back up your rootfs and restore it later somehow. Still didn't see any concrete instructions on how to do it though. Would be extremely useful for doing various risky things with the OS. After all, my repartitioned N900 with /usr on eMMC (thanks ruskie) did survive PR1.1 upgrade (did it via apt-get, then edited init scripts before rebooting), but I'm not so sure about forthcoming PR1.2...