I am not sure if it has been requested before, but it struck me as a neat idea. We have all sorts of stats about everything, why not one more?
I think it would be interesting to see how many battles I have challenged each day for the last month or so. Just a raw number, like 531 would suffice. And you could maybe go longer. You could just have for example: "February 06: 15238 battles challenged."It could just be something you could use to compare how active you are against another player.
Other variations on this idea would be to show how many battles you were challenged each of those days as well. Or how long you were on CB each day, or the total time you were on CB for the month (that one might be depressing though). I'm not sure how feasible any of those are, but I would be interested to know them. And yes, I know I could write down after each day the results of my 24 Hour Battle Summary, but why not just automate that and make it available for everyone?