Can you see advertising?

While preparing a presentation for Rome University, I took many snapshots of MySQL web site. I asked for review, and Colin pointed at the advertising that was in most every page.
Now that he mentioned it, yes. I saw the advertising. But when I was working with the live page, taking the screenshots, adjusting them with the Gimp, and inserting them into the presentation, I did not notice them at all.
I am blind to ads.
I must be the worst nightmare for advertisers. I have pop-up blockers and javascript filters in my browser, so don't see many of them, but the remaining ones are like a ink stain on the page. My brain registers the presence of an alien presence, and quickly instructs my senses to ignore it. If someone tells me that there is an ad in a given page, I have to look at the page twice, to put the ad into focus.
Why does this happen?
I guess that, after so much time spent using the web, I am trained to spot where the content is, and I filter off automatically all the distracting bits.
If the ad contains an interesting image, I may register that, and even remember it sometimes, but I have no idea of what they were selling with that picture.

For instance, I saw this image in the Singapore subway. I took a picture because it was cute. I can't remember what was advertised.
Now, if this filtering happens due to my frequent usage of the web, I wonder how many users have developed the same self defense and evolved into a Homo Sapiens Non Publicitarius, a particular breed of human being who has been saturated by ads and can't see them anymore.
Anyone from the same mutation out there?