artek - 12:19 am on Mar 20, 2013 (gmt 0)
We had similar issue with AdWords. The number of clicks form ads on the G search results pages almost doubled in the year where at the same time conversion did not go up at all.
Statistically it didn't make sense at all and we came to conclusion that the false clicks were mostly responsible for the increase of ad clicks.
You can also read about this problem here [ft.com]