I advertise in the weight loss/diet niches, and it's getting crazy.
Not only do they create new sites constantly, they also copy ad text from other advertisers. So you end up looking like a part of that spam ring.
One site I was promoting, was getting around 6,000 clicks per day before they moved into the niche. Now, it gets 150 clicks a day or so, and I had to increase the CPC by 50% just to continue getting any kind of traffic at all.
I hope Google does something about it, but I also hope they don't just ban all sites that have similar ads. The same goes for publishers.
I also saw them on many completely unrelated sites, so they seem to be trying to get any kind of traffic they can.