I've almost forgotten about kexec, but it really comes in handy as this beast takes an awful lot of time to boot. Not so with kexec:

$ uname -a
Linux v40z1 2.6.33-rc1 #1 SMP Sat Dec 19 02:25:22 PST 2009 x86_64 GNU/Linux
$ kexec -l /boot/2.6/bzImage.old --append="root=/dev/sda2"
$ date
Sat Dec 19 02:35:30 PST 2009
$ kexec -e
I'm in purgatory

Ubuntu 9.10 v40z1 ttyS0
v40z1 login: root
Password: 

$ date
Sat Dec 19 02:35:47 PST 2009
$ uname -a
Linux v40z1 2.6.32 #1 SMP Mon Dec 14 05:26:12 PST 2009 x86_64 GNU/Linux