The adSense blog has just notified everybody that it is now possible to modify the font of any adSense Adblock you are publishing on your website.

It is now possible to change the font face of any text in adunits in any one of the Latin character languages.  For now you can choose between Arial, Times new Roman and Verdana.
Of course this can be done when customizing an ad unit, just like when you would change the ad colours. This is done via the ‘Ad Display Preferences’ within your AdSense account and this will alter all fon types for all your current active AdSense ads.

You can also specify specific fonts per ad unit when using the ‘Manage Ads’ feature.

This opens up opportuinites for new optimization testing. Just like altering colours and positions, changing an Ads text may give you a slight increase in your CTR. We suggest experimenting with this and finding the font that is most profitable for you.

Good luck, and happy optimizing.