I agree with Gavin,
Just wrote an extent on a blog of some complete stranger that was debunking a scientist with 100% ad hominem attacks. Seriously, 100%. It didn't even mention the science except in quotes. Ad hominem is just counterproductive and leads to knee-jerk reactions and loads of bickering as this blog suggests. The fact that it has now come to entire arguments based on people's backgrounds is worrisome to me so I think is an important point to get across.