I started experimenting with metarouter on a RB450G running ROS 6.2, very cool stuff. If I build a MR running ROS or even openwrt how would I move it to another host or even backup the metarouter? I don't see anything under the Files menu and don't see an option to backup/export the metarouter VM.

there is no way on how to save metarouter explicitly, but this has to be done in steps:

for RouterOS:
save on host
a) /metarouter export
b) /interface virtual-ethernet export
on ROS guest:
c)/export (for all guests separately)
to restore do the same in reverse order and yo should restore the configuration

for non-rotuerOS guests
a) /metarouter export
b) /interface virtual-ethernet export
for non-RouterOS guest:
save relevant configuration of guest

to restore - create guests by importing relevant images and restore configuration.

It is not possible to export whole guest.