The first 'save the date' invite I received was to my friend Goodwin's wedding. The event was to be held in October on the banks of the Shenandoah (Had to put that detail in because it's such a lovely name), and the letter got to me in March or April. Though I couldn't make it to the wedding, I was given sufficient time to make arrangements.
About two or three years ago, Bombay galleries started sending out cards and emails with the tag 'save the date'. Without exception, they were for openings scheduled within a week of the mail's delivery. It isn't unusual now to get a 'save the date' invitation today for an opening tomorrow. I don't expect art shows here to be planned as far in advance as American weddings, but surely there comes a point at which appointment books should be presumed to have been filled, after which it becomes mildly insulting to ask for a date to be saved.
I used to be bothered by the use of 'vernissage' instead of 'opening' or 'preview', since the French term sound dreadfully snobbish. But now 'save the date' annoys me more, partly because the meme has proven so infectious.