Have you seen the new AdSense ad formats yet? If not, you can find out about them and see them in the official "Inside AdSense" blog. You'll definitely want to pay attention here folks.
So, my warning to ALL publishers is to check your sites and look at your ads carefully to ensure they don't look like your content too much, and also double check the new formats to ensure they don't look like the ads from other advertisers. In the image posted on the Inside AdSense blog, the square ad formats appear to resemble ads from at least one other ad serving platform - a fair bit more than they did before.
It's up to publishers to ensure their sites, ad styles and ad placements do not contravene policy, so spend some time this week checking your own sites for this new ad format - and take action before they have to issue you a warning...or worse, simply disable your account.