When the iPhone 4 came out alarms were going off at the wrong time even though the clock was set correctly I believe that issue is now fixed as my phone alarm went off at the right time
My 4s apparently knew DST was ending, but decided to change my time zone to "New York" so that the time remained the same! (I'm in the Central time zone). Restarting the phone fixed it, but I'm glad I didn't depend on it to wake me up.