The folks at WebmasterWorld are noticing Google testing a new AdSense font.
Truth is, I see it also and it is very sharp, crisp and it stands out more from the original font options.
Here is the typical AdSense ad font:
This is what I see now:
I am not even sure if this is a test now because virtually everyone sees the new font type.
This was first noticed a bit over a day ago in WebmasterWorld where the publisher wrote:
It seems that Google is testing new fonts in AdSense text ads. Starting yesterday, I'm seeing ads using the "Slabo" font family, a narrow, slab serif typeface. This font family isn't available in the AdSense font options, though.
Forum discussion at WebmasterWorld.