As web design trends evolve ( and as the devices users employ to access the Web provide more immersive experiences) the ad units that publishers require to monetize their digital properties must also change.
Google has just announced that a massive 300x600 unit will soon be available in publisher accounts. These half-page units are one of the fastest growing sizes by impressions (according to Google's recently released Display Business Trends - PDF) but while full of promise and pizazz, they are not without their limitations.
Integrating these much larger ad units is likely going to take some creative integration to ensure both advertisers and users receive an optimal experience - but that's only the tip of the digital iceberg. Google has made it known in the past that it does take page layout into account (at least to some degree) when ranking sites and these banners are bound to present some problems - we'll see how much as more publishers integrate them.
For those of you keeping track, Adsense now offers 20 different ad unit types - from leaderboards and skyscrapers to link units and squares.