I was asked to do this once on a return from China. My wife and I have had only one true, "secondary," in which we were asked to open our bags and the customs inspector took a cursory look around. That's two times out of more international trips than I can possibly count or remember.

One thing I've noted is that we are usually meticulous about documenting our purchases -- if we've bought a lot of stuff, I'll prepare a spread sheet that lists the item, the purchase price in foreign currency, the current exchange rate and the equivalent cost in dollars. I've had customs people comment, favorably and with amusement, about our list, but it's never been questioned. I do remember one time (back when we had money) that I bought Mrs. PTravel a fur coat in Rome for $5,000 or so. We listed it on our customs declaration and were fully prepared to pay the import duty. The customs officer looked at our declaration and just waived us right through.

I've never had an unpleasant experience with customs, even after it was brought under the DHS umbrella. However, I have routinely found some immigration officers, both as INS and DHS, to be arrogant, abusive and, in some cases, overtly bigoted.