iCal, Apple's highly-touted calendar program for OS X, is a piece of crap wrapped in a silky cover. It is unbelievably, unreasonably, idiotically slow (70 CPU seconds to load a few years of calendar file). And it's unreliable; today I crashed my Mac by making a mistake changing the battery, and it just silently lost all my calendars going back to day one.
I'll try it again in a few years when it's actually ready to use.
