I've thought about it. The traditional way to make the drink is to soak the root in cold water and the drink does not taste very good.
I'm not sure how to use it in beer. Adding it to the boil like a spice would seem to make sense but I'm hesitant to add it to the boil b/c the traditional way to make the kava drink doesn't involve cooking, just letting it steep in cold water.
I think the way that I will eventually try it will be to add a small amount to a finished beer. I'll pour a dark beer over some roots, let it soak for a bit, fish the roots out and give it a try.
The effects of drinking kava are...well...meh. But I do want to try it in beer.