in my quest to prepare for hacking git-gui, i ran cd .../git/git-gui git log . the result is ... unhelpful. apart from a few commits that were done directly in the git repo, there are only merges. notably, there is no trace of the commits that are being merged (and the way gitk presents this partial log is even more unhelpful). i'm speculating that this is the result of git log not handling the subtree merges in any way, with somewhat predictable consequences. i suppose there is overlap with the fact that --follow works only for a single file, which is also unfortunate. (a recent test case in the repo would be templates/hooks.)
