I have a quick and dirty way to detect if the FireFox AdBlock plug-in is blocking ads on your site. I am still not convinced it is a good thing to annoy AdBlock users. First, AdBlock users aren’t going to click on ads anyway. Second, AdBlock users are more than likely to leave your site if they are issued a nasty message. You aren’t going to change behavior with this.
I may start putting alternate messages up if my Google ads are blocked, so that the space remains.