I decided a little while ago to get much more serious about testing than I have been in the past. Last weekend, I had an inspiration and spent about fifteen minutes to setup a new layout for one of our sites: it was a clear winner extremely quickly. Enough of a winner that the size of our monthly cheque will be changing by a substantial amount (and already has even in just a week).
In looking through our reports it appears that one of the significant contributing factors has been the new adlinks unit. It's performing very well for us.
Could be the fact that it is still novel, could be the way we placed it/the way it fit very nicely into our site, could be related to the nature of the site, could be a variety of things.
I'm curious to hear how it is performing for other people.