Advertisements can be useful in generating income on for a web publisher, but annoying for the reader. To minimize the annoyance I am trying more selective ads. If you go to my Web Design notes you will likely see no ads.
But if you are referred to the same web page from a link on a commercial web site (one with COM or CO in the name), you will see ads. I did this by including code to check the referring URL. Additional CSS is used to adjust the page to make room for the ads, when required.
If the user enters the URL directly in the browser there will be no referring URL and so no ads will appear. Similarly, if they click on a link elsewhere in on my web site, or are referred from a GOV, ORG or EDU site, there will be no ads.
The reasoning behind this is that the people who find the page via a web search (such as from Google) are likely to be interested in the general topic and might find the ads useful. Those directed specifically to the site are more likely to be interested in the specific page content and less interested in the ads.
Hopefully the result is ads for those people more likely to appreciate them and no ads for those who do not.
I have also implemented the same technique on the ACS Digital Library. This was tricky as the digital library uses HTML frames. Simply checking the referring URL didn't work, as the referring URL of the web page displayed is always the digital library site. I had to insert code in the frame HTML to store the referring URL and pass it on.
Please let me know if there are problems with this. The code may not be foolproof, but if the only harm is to display an ad occasionally when there should be none, or not display one when there should, it does not much matter.
ps: One exception I make is for people using Google's Scholar search facility. Google Scholar has a COM address but I suppress the ads anyway. Academics are likely to grumble about ads and don't have much money to buy things anyway. ;-)