New Post: Creating Tasks per a User Defined Calendar

There is no "exception" trigger function that will prohibit execution of a scheduled task. Two thoughts on how to do this more manually:

1. Instead of scheduling using a single DailyTrigger, you could use 12 separate MonthlyTrigger for each month and then specify the days that year that are not known holidays. You would need to update the trigger list each year though and make sure to set an expiration date for each trigger for the end of year.
2. Have a script that will go out just before each holiday and set the task's Enabled property to false and then set it back to true at the end of the holiday.

I wish I had a better answer.