If you wanted to see how your link units were performing on a site or a page, you used to have to tag them with a seperate channel, but the results were skewed because there were impressions on the site and impressions once the actual page of link units was displayed.
Google has just updated their control panel and you can now run reports just on link units. And, it will show the page impressions, clicks, then the number of link clicks, and the Page eCPM. This makes it much easier to identify how link units are performing versus regular ad units or referral ads on the page.
Want to try out some link units and haven’t yet? Read Using AdSense Link Units in the footer & navigation to give you a good placement to start with.
Read more on the AdSense blog, along with a screenshot that ironically shows no link unit data, just where you change to show the link unit data. Do note that data is only available back to May 2007. But if you run a report trying to pull data including dates previous to that, it will end up showing no data at all due to a bug that the AdSense team is working on.