@vegas: notice that the matter here isn't the size in pixels of the banner, that is to be kept. What Mark0 means is that the current banners are too space-consuming due to lack of compression.
My opinion about this matter is that as long as the lack of quality isn't noticeable, it should be reduced. But i really don't make much fuzz about it because it's mostly loaded from opera's cache.
It might matter in terms of DC bandwidth, tough.