Just wanted to say thanks Ozh for this plugin. I have been googling how to show adsense adds only to my search engine visitors and it was either incompatible code issues with WP Super Cache or code that just didn't work.
Your plugin does what it says & was quite easy to implement in my theme. So I have only just installed it today and will test to see if my CTR changes if I don't display ads to certain visitors.
So thanks for the easy and just what I was looking for plugin.
Good luck with the plugin book.