I read a lot of economic analysis - obviously a complete waste of time from a system trading point of view! Dispersion charts are very common, even with "average percent changes" displayed on them; consider this speech given by Mishkin. It contains a whole panel of such charts with averages.
I like percentages. I think they are useful in system design and analysis because they lead you to expectations for the future rather than fictional back-tested equity curves. But percentages, in their usual form, have a problem that anyone in trading is familiar with: if you lose 10% you need to make 11.1(1) % to break even.
It's not symmetrical and it annoys me!