The AdSense for search fees that are referenced in the AdSense Terms and Conditions will not be applied to all publishers. Google incurs a cost for each search that is performed through AdSense for search, and generally we cover this cost through our portion of the earnings from user clicks. However, publishers with very high numbers of searches in relation to their revenue may have an amount deducted from their final AdSense for search earnings. We expect the number of publishers to be impacted by this to be very small - less than 1% will be affected.
The AdSense for search fees will never be greater than your AdSense for search earnings, so you won't ever owe Google at the end of the month as a result of these fees. Earnings from AdSense for content clicks will not be affected. The adjustment will take place at the end of each month, when earnings are calculated.