Prof. Eric Goldman [again! ;~)] reports there was another ruling in the US about trademark liability for purchasing keywords from search engines.
This time, "the court dismissed the trademark infringement claim for the keyword purchases because the purchases do not constitute a trademark "use in commerce"".
The case is Merck & Co. v. Mediplan Health Consulting, 2006 WL 800756 (SDNY Mar. 30, 2006).