Lame_Wolf - 2:33 pm on Nov 15, 2012 (gmt 0)
Yep, that is exactly what happens. I've just spotted one with just one advert in it, and a huuuuuuuuge space underneath.
Or might you end up with a 600 pix deep box with one normal size text ad in it?
(There are enough advertisers to fill those gaps many times over, so lack of inventory is not the reason.)