Many iPhone users noticed a OS bug yesterday which meant most alarms would not go off. This was tested a few times on my own iPhone 4 running the latest OS and confirmed to be the case.
This issue did not seem to effect ‘recurring’ alarms only individual ones but over at Engadget it has been said that this big will correct itself on the 3rd January anyway so users who are effected will not be for long.
Apple have sent a reply to Engadget about the issue which confirms the fix:
We’re aware of an issue related to non repeating alarms set for January 1 or 2. Customers can set recurring alarms for those dates and all alarms will work properly beginning January 3.