Even if you don't understand the basic concepts of the International Date Line, bother to read the article: it's not "a pattern that dates back thousands of years".

  The change comes 119 years after Samoa moved in the opposite direction.

What's going to be the date? Again, from the article you could see that they will skip from December 27th to December 29th, missing the 28th. So the date will be December 29th.

As to "a day isn't just some thing", a day is a 24 hour period as defined by how long it takes a planet to rotate on its axis. They aren't changing that, their days will still last 24 hours. Dates, however, are indeed just some thing, purely defined by humans, and there have been multiple different calendars over the years. See http://en.wikipedia.org/wiki/History_of_calendars

Samoa sits practically right on the International Date Line, this is the line where GMT -12 meets GMT +11, so that you are travelling forwards or back 24 hours whenever you cross over it, depending on your direction. Therefore, whichever side of the IDL they chose to base their time and date on, the time will still fit the day as we know it (i.e. dark at night). And, whichever side of the IDL they chose to base their time on, there will always be other islands very, very close to them that are 24 hours (i.e. one whole day) away from them.

Ultimately, the only difference this makes is whether their weekends coincide with those of the Americas, or those of Australasia. Since, in the past 119 years, their businesses have moved from mostly dealing with the Americas to mostly dealing with Australasia, so it makes sense to move back to being in sync with Australasia.

1) They just picked a new time zone which is more convenient for doing business with their neighbours. No dates disappeared, the new time zone just happens to be off-set 24 hours from the old one. Timestamps can still be converted between the old and the new time-zone, just like you can do the conversion for any other pair of time-zones.

2) The Gregorian calendar was introduced in 1582, not "thousands of years" ago.

Did you... read the article?

For quite some years every other Sunday I'd leave home1 early evening and arrive at home2 early Tuesday morning, having travelled on average about 21 hours (all those mandatory inspections of my underpants, you see), thereby skipping an awful lot of Mondays.

A day really is just a thing: I'm not any younger.

While you're right that crossing the IDL doesn't make you a day older or younger... there is a slight flaw in your logic. In order for you to have gone forward a day every two weeks, you must have come back a day in between, as well.

After all, it's possible to fly around the world in less than 24 hours, but you can't use that to travel forward or backwards in time, you can only ever get to a maximum of 24 hours ahead or behind of another place.

Perhaps I was too dry: everything you say is true, but you kinda missed the point ;)

Edit: In retrospect realise that wasn't particularly helpful. I skipped an awful lot of Mondays for which the only consequence was utter joy at the two cocktail hours every other Saturday. Contrary to the great grandparent, a day really is just a thing.

Sorry, I wasn't clear enough - I didn't miss the point you were making, and I completely agree with it (one of my other comments somewhere on this page makes that same point), I was just pointing out the flaw in your example that travelling forward through time zones many times won't make more of a difference than doing it just once.