Here is an interesting, very fact specific, federal case in which the forensic examination of a computer for child pornography was suppressed. The accused had admitted possessing child pornography, showed the police his computer, but refused a search of it. The police took the computer. Then it sat around for about three weeks before the police got a search warrant. The court does caution the case to be fact specific.
United States v. Mitchell, __ F.3d ___ (11th Cir. 2009).