Don't know about how many of you do this, but I'll bet more than one or two. Every year around Christmas, my family will crack and eat close to 50 lbs of various kinds of nuts. Everything from English Walnuts, Almonds, Pecans, ect.
I started keeping the shells instead of throwing them away, and it lets me replace my tumbler media, several times a year for free. Just be sure to throw away partially filled shells and use only empty shells and don't let any of the nut itself get in there. The nut will turn to oil and wind up on your cases.
Not sure how much media costs, as I have never bought any, but every dollar counts when you like to shoot a lot.
My brass probably isn't as clean as some of the ceramics or what not could get them, but they look as good as factory when I re-load them.