Yeah... that's super annoying... there's maybe some exceptions, but it's usually not that hard to at least just put a height on the ad, so it's a blank rectangle until it finishes loading, and then it's an annoying rectangle, but it doesn't need to change shape.

Also, on my hate list, articles with an ad under a paragraph that somehow moves to the top when it gets half-way up the screen or something, so it's really hard to scroll down while reading. Blerg.