Clarence - 2:55 pm on Dec 9, 2012 (gmt 0)
If you're using link units on your site, unmatched ad requests might be higher than expected. This is due to the way we count a matched ad request for link units. A matched ad request for a link unit is only counted if the user clicks on a term in the link unit. If the user doesn't click, the ad request is considered unmatched. As a result, coverage is lower for link units than other ad units.