A bug in iOS 4.x seems to be rendering iPhone alarms useless after January 1st, 2011 (today), according to Engadget based on numerous tweets. 9 to 5 Mac reports that testing indicates the problem will self-correct on Monday, January 3rd. Since this fairly serious issue only affects one-off alarms, users are encouraged to change all events to repeating alarms for the next two days until things return to normal.

A similar, but not identical, bug appeared in early November during the switch from daylight savings to standard time. In that case, while alarms continued to go off, they were ringing either late or early.

Source: Engadget, 9 to 5 Mac

Via: Phone Arena