I got tired of tires going out of balance on me, so I decided to experiment with airsoft BB's. About two years ago, I balanced the 235/85R16's on our Comanche with about 5 oz per tire of .30g BB's. The BB's didn't help the 47mph shimmy that's always been there, but it did take care of higher speed balance issues. At this point, I'm calling it a success, and blaming the shimmy on alignment, since it didn't change when I went from proper weights to BB's, and doesn't change with tire rotation either.
I just put new LR G tires on my trailer, and tossed in 6oz of .28g bb's when I mounted the tires. Zero noticeable shake up to 70mph. Success. With that, I decided to try them in my truck too. The 265/70R17 New Fun Country tires were perpetually out of balance by just enough to bug me at 70-75MPH... I mounted up some 285/80R17 ST Maxx's a few weeks ago and tossed in 6oz per tire again. It's only been on a few trips up to CO, but it runs baby's butt smooth up to 75.
At this rate, I'm never going back to weights.
I did hear that the BB's can "bounce around" after a bump, resulting in some additional "bumpy road" feeling. I have not noticed this on my truck, nor on the comanche. Perhaps it becomes more of an issue with really big tires on a lighter vehicle...
As usual, YMMV