Finding files to back up

[Mark Carroll <mark@chaos.x-philes.com>]

Being of the belief that a fresh reinstall can help to spring-clean my
machine, my usual approach to backups is to preserve my package selections
and the files that I've added (e.g. in /home/) and modified (e.g. in
/etc/) that wouldn't be recovered in a simple package reinstallation.

I see that dpkg can tell me about associations between files and packages.
Can I somehow get a list of the md5sums of the package maintainers'
version of the files so I can tell if they were modified? Maybe things
aren't as simple as I'm imagining?

-- Mark