Suppose you are writing a appointment tracking system, and, at some point before the olson tz database has been updated with this change, the user in the Samoa timezone creates an future appointment for Jun 2, 2012. That would be stored in UTC.
Now, you upgrade the olson TZ database file on your server to a newer version, which incorporates the Somoa tz change. Now, without any user input, the appointment is suddenly on Jun 3, 2012! (because the same UTC date, with the updated TZ database, is Jun 3, 2012)
Is that what a user would have expected if they created the appointment for Jun 2, 2012? I would say no. But that said, what if the appointment was for Dec 30 2011? That date no longer exists, so it would have be pushed ahead automatically.
Conclusion: time zones are hard
Past events had the local time, UTC, and time zone entry stored. Storage isn't much of an issue and it helped to keep things straight. Future events were only stored in local (8pm Dec 12, 2012) with time zone. Calculations were done on UTC with future events computing UTC on the fly. Reporting and actual day something occurred was kind of important. A day skipped would be an issue.
Even simpler problem is not so easy to handle in software: if you save dates in UTC, once DST start date changes, all your meetings move one hour, but most meetings are scheduled in "local" time, i.e. dentist still expectes to see you at 10am.
http://mm.icann.org/pipermail/tz/2011-December/008457.html
EDIT: Correction, that thread was about Tokelau and not Samoa. The Samoan change seems to already be in the latest version of the database.
I know Jews wouldn't, and I doubt Muslims would, but I don't think there are any Jews there anyway, not sure about Muslims.
My question was what does Christianity do, and I guess no one here knows.
I'm not super familiar with the Muslim rules, but I know the Jewish rules have their own date line that does not correspond to the international one.
I don't know what the Christian rules are about the international date line and that's what I was asking.
