Google AdSense released Ad Links on June 09, 2005 and publishers had plenty of time to test them out. A thread at WebmasterWorld named AdLinks bringing most of the revenue? Can anyone confirm? shows how for some it does well, and for others, it does not to well.
One member reports that "Ad Links have a really low CTR compared to the other ad blocks but it brings in about 1/5 to 1/4 of my income." While an other reports that "for me, one small AdLinks block brings nearly half my AS revenue."
As you can tell, and something AdSense professionals like JenSense has been telling everyone, it all depends on the site, audience, and implementation. You can not compare site A to site B, there are just too many variables.