Hi, What a wonderful Topic ... ;)
I was searching many hours und tried lots of tools to create statistics but i think the simplest way is:
exiftool -q -S -aperture . 2>/dev/null | grep -v ===== | sort| uniq -c | sort -nr
Of course, the win tool exifviewer 2.x outputs histogram graphs of the iso, aperture etc.
I think phils proposal with the export to a tab separated table is another good base to do such kind of stats.
My problem now is to build the graphs from the data at commandline!