Unfortunately I sometimes wake up with no alarm going off, think to myself "hmm, where's the alarm? what time is it?", look at the clock and realize that it's 4 hours later than I intended and the alarm has been turned off. Since I have no recollection of turning off the alarm, it isn't really a matter of discipline :(
Edit: Of course, I'm not suggesting that this is a deal breaker, or that I've 'given up', just that it's not always as simple as "just get up when the alarm goes off." I also have been known to pass the turing test in my sleep. I once convinced my wife that I had the day off when she tried to wake me up... Yea, I was really late that day.
I once got up, ready, into the elevator, down to the street, bought a coffee and took a sip, looked around (dark, busy intersection not so busy), swore and then went back to bed. As far as I know I was totally coherent the whole time to everyone around (wife, doorman, coffee-shop-girl, etc).
Stress factors a lot into it for me. If I'm having a good week hardly anything strange happens in my sleep.
Edit: Of course, I'm not suggesting that this is a deal breaker, or that I've 'given up', just that it's not always as simple as "just get up when the alarm goes off." I also have been known to pass the turing test in my sleep. I once convinced my wife that I had the day off when she tried to wake me up... Yea, I was really late that day.