I'm not a fan of advertising to start with, especially in the online era, since I find that advertisers tend to pigeonhole people in a deliberate attempt to limit our world-view (to coincide with their products).

Another issue is that I work with other people's children and tend to play it safe with what I bring into the classroom. I can control the books on my ereader, so that's not a problem. I cannot control the ads, so that is a problem. Yes, it is an issue. I've seen teachers bring materials into the classroom without pre-screening it, and they have suffered through a few non-so-comfortable moments because of advertising on scraps of newspaper.