Apple has published a support page that recognizes the problem with alarms after the changeover to standard time last week.
The problem appears at that some users are experiencing the iPhone alarms ringing an hour later than was asked of them. It is solely related to repeated alarms, so the solution is not to repeat the alarm, but to turn it on manually every day.
IOS 4.2, which is coming up, correct the error. Yet there is no official date, but since Apple support document writes that from the 7th November can set alarms to repeat again, it appears that this particular day is the day when IOS 4.2 comes officially.
You'll find Apple's support page on the problem here.