A recent decision by the United States Court of Appeals in a case against Embarq (now CenturyLink), in relations to the use of NebuAd for behavioral advertising clears Embarq, the ISP (background - here, here).
Judge Harris L Hartz concludes: "The alleged interceptions occurred when Embarq authorized NebuAd, Inc., an online advertising company, to conduct a technology test for directing online advertising to the users most likely to be interested in the ads. Exercising jurisdiction under 28 U.S.C. § 1291, we affirm the district court’s judgment. Although NebuAd acquired various information about Embarq users during the course of the technology test, Embarq cannot be liable as an aider and abettor. And it was undisputed that Embarq’s access to that information was no different from its access to any other data flowing over its network. Because this access was only in the ordinary course of providing Internet services as an ISP, this access did not constitute an interception within the meaning of the statute".
See here, and below.