Installed ('copy-nand') rawhide-xo image 20090303.img on my XO.
The boot process (with the 'check' key) stops after the lines:
sd 0:0:0:0 Attached scsi generic sg0 type 0
scsi_scan_0 used greatest stack depth: 2212 bytes left
[ About 11 lines earlier is the output message:
mount: unknown filesystem type ' jffs2' ]
mikus