I have a calendar in my kitchen. I bought it for 50p in St Ives market, and it shows coastal scenes of the UK. On it, I scrawl appointments, parties, my work schedule, and when my parents or the in-laws are coming round so we know to tidy up in advance. I share it with my husband, who never writes anything on it, and I doubt even looks at it. Occasionally, the cat will bash it, or it'll fall off the cupboard handle to which it is tied to. Come December 31st, it'll be torn up and placed in the wheelie bin for recycling, and a new one purchased under a strict criteria (is it too girly for a household that is only 33% femine (the cat being the second masculine member), can we look at it all year and not get cross, does it cost less than a bottle of wine). I write in code to prevent awkward questions from visitors, mostly my parents. Holidays are never marked as such in case burglars see it, again to prevent my parents worrying that hoardes of hooded teenagers clutching crowbars are just waiting in the hedge to steal our aged games consoles, scruffy paperback books and the tv that came off the ark.
I can see the point in an online, shareable calendar tool. But I quite like the mystery of knowing people can't tell when I'm genuinely busy or if I'm just avoiding them. It may be useful for my work to have something set up for the students, but at the moment we use facebook and a piece of paper taped to the office door for unusual or brief closures, usually for lunch.