Sources from approx. Wed Jan  9 12:04:49 EST 2008, booting a xen3 domu 
results in:

Using config file "/usr/pkg/etc/xen/babylon".
Loaded initial symtab at 0xc048a2f4, strtab at 0xc04be780, # entries 12486
Started domain babylon
                      panic: kernel diagnostic assertion "obj == NULL || 
mutex_owned(&obj->vmobjlock)" failed: file 
"/usr/src/sys/uvm/uvm_page.c", line 1076
Stopped in pid 0.1 (system) at  netbsd:breakpoint+0x1:  ret
db> xenconscn_getc(): not console

And it locks up hard.

Sarton