In summary
Loopback mounts — don't do much.
Loopback mounts with NBD and nbdkit — infinitely flexible.
Lots of plugins, or write your own.
nbdkit 1.8 now available in all major Linux distros.
https://github.com/libguestfs/nbdkit
This talk:
http://git.annexia.org/?p=libguestfs-talks.git
This presentation software: Tech Talk PSE 1.2
Any Questions?