Much like +Martin Post
, I believe most people have subconsciously learned to treat ads like white noise in the background and don't really even notice they are there.
In those occasions where a site has gotten obnoxious with the number of or type of ads, I think the ultimately do themselves more harm because less and less people will chose to visit those sites.
We can ignore the existence of most ads in the course of our daily activities and frankly appreciate the one's that are correctly targeted when we are actually experiencing a specific need.
Personally I am thankful for this business model. It's allowed companies like Google fund the development, release, and support of some amazing and useful technologies that we as the general public get to us for free. If that's not conducive to a truly democratized open internet experience, then I don't know what is.
They alternative would be too expensive for the general public, would stifle the ability to finance innovation, and would create of world of have and have-nots.