Google's paid clicks increased by 18% Y-o-Y in Q4 2010

"Paid Clicks – Aggregate paid clicks, which include clicks related to ads served on Google sites and the sites of our AdSense partners, increased approximately 18% over the fourth quarter of 2009 and increased approximately 11% over the third quarter of 2010.
Cost-Per-Click – Average cost-per-click, which includes clicks related to ads served on Google sites and the sites of our AdSense partners, increased approximately 5% over the fourth quarter of 2009 and increased approximately 4% over the third quarter of 2010.
TAC - Traffic Acquisition Costs, the portion of revenues shared with Google's partners, increased to $2.07 billion in the fourth quarter of 2010, compared to TAC of $1.72 billion in the fourth quarter of 2009. TAC as a percentage of advertising revenues was 25% in the fourth quarter of 2010, compared to 27% in the fourth quarter of 2009.
The majority of TAC is related to amounts ultimately paid to our AdSense partners, which totaled $1.74 billion in the fourth quarter of 2010. TAC also includes amounts ultimately paid to certain distribution partners and others who direct traffic to our website, which totaled $333 million in the fourth quarter of 2010.
Other Cost of Revenues - Other cost of revenues, which is comprised primarily of data center operational expenses, amortization of intangible assets, content acquisition costs as well as credit card processing charges, increased to $877 million, or 10% of revenues, in the fourth quarter of 2010, compared to $688 million, or 10% of revenues, in the fourth quarter of 2009.
Operating Expenses - Operating expenses, other than cost of revenues, were $2.51 billion in the fourth quarter of 2010, or 30% of revenues, compared to $1.78 billion in the fourth quarter of 2009, or 27% of revenues."

Source:  Google's Earnings Statement for Q4 2010, 20th January 2011