A CPUL is a rate based on Unique Landings, offered uniquely by AOL. We tested this out with a campaign back in September and have been booking it since.
It's a bit limited in terms of retargeting (it doesn't) but the performance far outweighs. You would think the CTR would be low on a placement like this, forcing through more impressions but our most recent campaign is performing at a CTR of 0.09%. AOL is obviously doing their best to optimise - one way to get a network to work even harder!