Currently sitting in the Atlanta airport waiting for a connecting flight. I flew in from Mexico City, and I was lucky enough not to be searched by Border Patrol. Here's what I think contributed to my success:

1) A full flight that arrived at the same time as another international flight, and the more people there are going through Customs, the more likely they're not going to search you

2) I handed the agent a US diplomatic passport. Pretty easy to get waved though if you're a fellow gov type