The randomness of ad-clickers

I run ads on some of my sites and I try to keep them as closely related to the contents of the site as possible, for obvious reasons.

I've been trying out some of the new Amazon widgets on one of my sites, in particular the Context Links. These ads scan the content of your page and offer ads to match the content. In theory. Of course, they can only look at the individual words themselves, buy they do a reasonable job.

The content of the site in question is flight simulation. So, imagine my surprise when I looked over the orders received as a result of these ads for the past week, only to discover that only one item ordered was flight simulator related. The other items that visitors had ordered had absolutely nothing to do with the content of my site. My question is not why Amazon served those ads so much as what made a visitor to the site click on an ad and order an item that had nothing to do with the site they were on!

I'm not complaining, of course. But I do find I'm starting to ask myself if it's really worth my going to the (considerable) effort I currently do to ensure appropriate ads are shown on site.

Anyone else experienced this?