My iPhone4 reset itself to the new time this morning, no problem - but my weekend alarm, which is set to go off at 8.15 every Saturday and Sunday didn't go off till 9.15!
Have googled & found this happened in Australia last week and apparently it's only a problem with recurring alarms, ie those set to go off every Sunday or every weekday.
I've just done a test and resetting the alarm today, ie after the clock change, doesn't help, if you want a recurring alarm you need to set it an hour earlier than the time you want.
Alarms that are only set to go off once are fine.
Apparently Apple are working on an update to fix it.
Not sure if it's only the iPhone4 or if it affects 3G/3GS phones with the 4.0 software upgrade