Many sites that rely on ads as a source of revenue place them in locations that can trick a visitor in to thinking the ad is part of a website intra-link or, in other words, a link to another part of the same site. The thin horizontal Google Ad strip that looks like a navigation bar is particular suited to this strategy for this. The AdBrite ads are possibly the best, most annoying version of these stealth ads - they replace several words in the page with links to advertisers' pages.
However, you may notice that I host no such deceptive ads. That's because I know what it feels like to click an add thinking that I'll be brought to a page that was intentionally linked to by the author. I get frustrated with the page author for placing such a deceptive ad.
On the other hand, I am aware that certain individuals enjoy rewarding bloggers for a good article by clicking ads on the authors site, so I actually do leave one up, it's just somewhere that isn't irritating or deceptive.
In the entire lifetime of this blog, I have made 31 cents. As you can see, I'm not exactly in it for the money. I just want those few people looking to support quality blogging a chance to do so.