Generally haven't had a problem with last-minute (24 hour) purchases or one-ways. But then again, I'm a pretty heavy traveler on the airlines where I do that.

The last time I can recall having the SSSS for "last minute" was 2004 where DL canceled a flight and moved me to AA, which treated it as a last-minute, cash purchase... resulting in an SSSS. My AA status didn't apply because they had to add my FF number at the gate.