The amd64 version of -BETA4 doesn't completely boot under
qemu-system-x86_64 -- it hangs while trying to mound md0 as
root. The i386 version of -BETA4 does work under
qemu-system-x86_64.
Note that if you want to try this, use the -no-kqemu switch
as kqemu with the 64 bit qemu crashes the system.