In short the most important point of note is you can’t have on your site other ad’s that look like google ad’s, even if they are not contextually targeted.
I’ve already heard from a number of publishers that if given the choice between AdSense and YPN that they’ll jump to YPN because of the less stringent requirements – this change has put one too many hoops to jump through in front of some publishers.
AdMoolah makes the point
But what is considered the same color, if you have AdSense in dark green and Chitika ads in light green, is that different enough? If you always use leaderboards for AdSense and skyscrapers for Yahoo, is that different enough? Is adding a border enough?
There is going to be a lot of talk about this on the forums and in blogs. People are not going to like this.