One of our Australian forum members, TrAJik let us know that his iPhone alarm failed to wake him up this morning, January 1, 2011 (Australia time) and doing a quick look around the web it seems like he is not alone.
The iPhone had trouble with repeating alarms back during the change to Standard Time
so this could be the same bug rearing its ugly head again.
UPDATE: According to comments below, this affects **ONE TIME ALARMS* rather than recurring ones, so the opposite fix should work:
iOS 4.2 fixed that bug. Will we have to wait for an iOS 4.3 this time? If you're experiencing the problem and if you've found any other fixes, let us know in the comments below or help trouble shoot in our iPhone Forums.
UDPATE 3: Engadget confirms it's one time alarms that are causing the problem, not repeats.
UPDATE 3: 9to5Mac says the bug fixes itself on January 3.