At first themed units seemed like a good idea so I went on and enabled them on a decent earning adsense account. Of course when you enable them, they override your normal settings. That means you end up with a bordered unit with a graphic watermark in it’s background. This is bound to lower your CTR in most cases.

In my case there was a decrease of around 5% in CTR which means a lot less clicks and subsequently a lot less money. Disabling them takes some time before it takes effect but I immediately saw an increase in CTR after disabling them. The moral of the story is that you should stick around with your regular boring non-bordered ad units.