US Holidays calendar is broken. Why?
I use iCal for work, but it's growing steadily less useful for that purpose. Why not group US Holidays into four separate calendars, then let users decide which are relevant to them?
US Federal Holidays
Exactly what you'd think—only official government holidays, when banks, schools, etc., are closed.
US Secular Days of Note
Not actual holidays, but dates people might not want to forget, regardless of race or creed: First Day of Daylight Saving Time, Tax Day, Election Day, etc. A case could be made for including Mother's Day and Father's Day as well.
US Non-Federal Religious and Cultural Holidays
Lunar New Year, Good Friday, Easter, Orthodox Easter, Passover, Holi, Eid al-Adha, Juneteenth, Kwanzaa, Ashura, etc. As the US becomes more multicultural, this calendar will grow increasingly (and frustratingly) dense. If you observe one of these holidays or work with someone who does, you need to have it on your calendar, but if not, you probably don't.
US Garbage Holidays
Stuff that can be safely ignored: Groundhog Day, April Fools' Day (I personally observe this religiously, but c'mon), Cinco de Mayo (a feast day for local news anchors, but not a major holiday in Mexico), Flag Day, etc. Don't worry about missing St. Patrick's Day; green beer will always find a way.
Or you could include everything and just make the calendar customizable, so people can delete what they don't need. You're a big tech company. Surely you can figure it out.
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PS Regardless of one's religious sympathies, can we agree that the following message should never appear on an immovable date on the calendar: "The exact date of this holiday is difficult to predict precisely; this is just an approximation." You might as well have a little animated cloud hovering about, shooting holiday bolts at random dates in the general vicinity. It would be equally useless but a lot more fun.