I have, and it's lovely. But I have no control when drinking it, and I'm also doing Weight Watchers, so the 8 points for the bottle of chocolate milk was getting too "expensive" in terms of my daily diet.
I've been experimenting with various electrolyte replacement things while I'm running now, and those have eliminated my strong need for the chocolate milk, though I think I'll have DH bring some in our cooler backpack when I do the TOT 10-miler. I figure I'll be able to "afford" 8 points after that.
But anyway, I definitely felt a difference on the days I ran and drank it vs when I didn't.