tl;dr Calendaring is the only program that requires distributed coordination in the Microsoft office suite, so it is the hardest to make. Can't argue with that

tl;dr Calendaring is the only program that requires distributed coordination in the Microsoft office suite, so it is the hardest to make. Can't argue with that. But all of the difficult problems mentioned in the post are difficulties with any distributed system, not specific to calendar at all! Microsoft has probably been having those same issues with Word, Excel, even Powerpoint as they have been working on making them collaborative for a long time now...