In McGinley v. Florida, 2010 WL 5421320 (M.D.Fla. 2010), the prevailing party sought to include mediation costs as taxable costs recoverable under 28 U.S.C. § 1920. The court said they were not recoverable, which is not surprising given that the statute is fairly specific on what can be recovered, and mediation costs are not included. I guess you have to admire the attempt.