I admit I advertise with a few 'second tier' PPC providers. While the level of fraud is generally higher than the big players like Adwords and Overture, I am still usually able to eek out an acceptable ROI.
I monitor the clicks received from these PPC providers closely and notice that a large number of them have referers which point to fake search engines.
Basically when you go to their URL you get a search form and when you search for anything you either get no results, go back to the home page or get redirected to an adult site.
I would be guessing others would have noticed this too?
I notified the PPC provider once but it really is a hassle having to extract the relevant lines out from my logs and describe the clicks received when I'd rather be working on my site.
What are you using to extract the referrers from your logs? In case you didn't know, there are a variety of tools available (open-source and commercial) that you can use to automate and simplify the task.