I recall putting Adsense image ads on some sites a little while after they were launched and the results were so off-topic I dropped them immediately. I tried to find some current coverage on this subject but everything I found is from years ago.
I have a couple of sites with very "wordy" pages that would benefit from some images to break up the flow and image ads might just do that quite well. However, I don't want to end up with just one or two ad images occurring over and over again, or very off topic ads. It will look stupid if the page is about New York airport transfers and the ads are about discounted Icelandic hotels.
What is your current experience? Is there a decent inventory of image ads, is relevance matching OK and how do they compare with text based ads for generating income?