Hmmm.... I've tried that. I've tried mkinitrd -r /dev/sdb1 too...
The problem seems to be me having root on a SATA-drive....
mkinitrd fails to find the sata driver necessary to mount your root disk. See
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=263169
Workaround is to add your sata driver to /etc/mkinitrd/modules and rebuild the initrd.
What I _really_ do not understand is why this is not seen as a serious problem.
Regards
Harri