As Kent Scheidegger notes over at Crime and Consequences,the U.S. Supreme Court has granted cert in Herring v. United States, No. 07-513. The Question Presented is:

Whether the Fourth Amendment requires evidence found during a search incident to an arrest to be suppressed when the arresting officer conducted the arrest and search in sole reliance upon facially credible but erroneous information negligently provided by another law enforcement agent.

This raises the interesting question of what sort of mens rea does the Fourth Amendment envision. It forbids "unreasonable searches and seizures," and the Court has generally found that reckless behavior by police officers is unreasonable. Dropping down to negligence is a bit closer, but there is language in various Supreme Court opinions about "objectively reasonable officers" -- officers who presumably are not negligent. This one should be interesting.