I always wake up just before it goes off. Last night I forgot the turn it on before falling asleep (first time I've ever done that) and I woke up two minutes after the usual time. I'm a relatively light sleeper. And I usually end up waking up three or four times between 3am and 6am. Hasn't really been an issue, don't know why. I usually go to bed around midnight, so maybe I don't get enough sleep (4-6 hours a day)... seems odd that that would make me wake up earlier/easier.
How about you guys?