Thanks for etckeeper; I just used it in anger for the first time. I don't know for a fact that it really made my life better, but it makes me feel better. The story: I applied the usual security upgrade to my desktop box, and after rebooting, noted with dismay that my monitor, which had previously been happily running at 1280x1024, was now running at 640x480. (Typical Linux story.) So I poked around, and dimly remembered that I could run 'dpkg-reconfigure xserver-xorg', which I did. (I realize that's probably not the best tool for what I was doing, but it's all I remembered). That worked -- the monitor is now back to its old 1280x1024 self. Naturally the xorg.conf file is totally different; both the current version and the old version are utterly incomprehensible to me ... but the point is I've got a record of all of them, plus a comment explaining what I did and why. That's why etckeeper makes me feel better. Thanks again.

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Oops, it just saved my butt again. I swear I'll try not to append to this comment every time it proves useful ...