Carnivore/Echelon will never be introduced as evidence in court. These are tools of war. When they were hunting Bin Laden, they weren't planning on taking him to court in the end and introducing his emails as evidence against him...
That's precisely why ordinary people don't need to worry about what information is collected by Carnivore/Echelon. The results are too valuable to risk disclosure by introducing them into evidence for prosecuting run of the mill crimes. It's highly unlikely that agencies like the IRS even have access to this information for those reasons.
