I have dealt as a prosecutor and a defense lawyer with hundreds of warrants, and I can count on one hand the number of times the cops only took what was mentioned in the warrant. As a fed, I used to have long, complex discussions with agents explaining the scope of the warrant and what they could and could not take. The agents would nod as if they understood and then proceed to seize whatever occurred to them that day - ten-year-old receipts, takeout menus, whatever.
http://randazza.wordpress.com/2009/04/02/holy-crap/#comment-10536