From ClickZ
The conclusion: SEM campaigns must target both natural and paid components of the SERPS
+Women vs. Men: Women click more on paid ads vs natural search results
+College degree vs. non: Non-degreed clicks more on paid ads
+Frequent User vs. Occasional: Frequent Internet users click on natural listings over 65% of the time
+Experienced User vs. Newbie: Experienced users click on natural listings over 61% of the time