And a small script called git-diffl in your path:
/.../
Thanks for the effort, but that was a tad too kludgy for me (doesn't work with multiple dirs, for instance). I hope they'll add an option to git-diff eventually.
It clutters the diff output, IMHO. I.e. the diff heading already mentions the two hashes the diff is between. But it's a matter of taste, of course; I'll play around with it a bit and see what is workable and/or desirable.
Would be best if git-diff didn't expand when diffing (considering that the expansion is done after checkout I reckon that's what one would get anyway, unless they actively do the extra work to expand $Id$ before diffing too).
The usefulness is in bug reports etc, so working expansions are most important in dists. Can occasionally be useful in bug reports between developers as well I guess, but of course anyone is free to disable expansion in one's own trees. Still think it should be the default, though.