I got SSSS'd yesterday. I was travelling YYJ-SEA-BOI-PDX-YYJ and I had the SSSS on each boarding pass. In YYJ it didn't make a difference and in SEA I got the pat down and search at the departure gate. My BOI flight ended up cancelling, so I didn't get to enjoy the extra security at every other airport I visited (even though I later did SEA-YKM-SEA).