Not the same exact problem as the original poster, but the topic title fits so i'm putting this here.

The Google banner ad that i encountered runs vertically and not horizontally. This gives a very bad look to the forum home page, as it looks empty. (admittedly, given the recent forum update, i thought everything was missing).

I suppose they are only using the alloted area for a banner ad, but by going vertical they are killing a bunch of space. Can you specify that advertisers run only horizontal ads in these places?