How to determine which config files I have changed

[Paul Cager <paul@paulcager.org>]

I would like to be able to create a list of all of the configuration 
files I have changed / created since installation. Mainly to make it 
easy if I wanted to rebuild my system from scratch.

I can get a list of installed packages easily enough (dpkg-query).
I can use the cruft package to find files I have added to /etc (and 
other places if necessary).

But I'm not sure of the best way to generate a list of files I have 
changed. I could use "dpkg --contents" for each package to get a list of 
files in the package and compare timestamps/sizes. But this only works 
if the ".deb" files are still in /var/cache/apt/archives. Is there a 
better way, such as cached MD5 sums somewhere?

Thanks,
Paul