Entered US from Canada without having to reclaim checked bags for customs inspection.
Yesterday something interesting happened: I flew into the US from Iceland with two suitcases, but did not pass the customs at any step of the way.
My route was: KEF - YYZ - YVR - SJC. Operated by Air Canada for the entire journey (purchased via United).
KEF to YYZ: I passed Canadian immigration control (but not the customs) and continued on to YVR via domestic.
YYZ to YVR: no need to do anything with the luggage
YVR to SJC: I passed US immigration control, but did not have to retrieve and re-check the luggage - it was transferred automatically by the airline.
SJC: it's a domestic flight from YVR, so no customs, of course.
At no point in the journey was anyone interested in the contents of the bags that were traveling with me. Of course, they were still scanned as they were routed, but no usual full-blown customs check when you enter US and either exit the airport or re-check the luggage and continue on.
Apparently this is pretty new: you used to have to get the luggage at YVR and check it in again, but no more.
Pretty neat!