Other than when they used to come door-to-door, very little. A few years ago I had a friend who had a Doctor of Theology degree and he used to love it when the JWs came calling. He'd invite them in and make them a hot drink, but he'd make it extra hot so they couldn't drink it right away. Of course having accepted the drink it would have been rude if they had left without drinking it, so he had a bit of extra time to explain things like why their translation of Scripture was an inaccurate rendering of the Greek and Hebrew (needless to say he was pretty much fluent in Greek and Hebrew, along with a few other languages for good measure). Sadly he couldn't do it very many times before they got wise and stopped visiting him.