I've been flitting around a few different webmaster-type forums over recent days and one of the popular requests is 'please review my AdSense placement'. It's amazing how many people are still associating images with AdSense ad units - it's a definite no no.
The human eye has a natural preference for colourful image over boring text, so if you associate images with your ads you are drawing undue attention to them. In particular you must avoid any implication that the ad and image are one and the same thing! On pages with lots of small thumbnail images - a photo gallery for example - publishers should use borders around their ad units to physically seperate them from the images. Ideally, ad units should not be included in the same border as an image.
Guidance clarifying the situation was issued in the official AdSense blog not long ago.
If you think this indicates that Google are trying to meddle even more in how webmasters manage their sites you're probably right!