Although I’m tempted to try Google calendar because I like playing with new toys, I don’t really need to use it because we use Outlook shared calendars at work and I don’t have enough of a social life to need to use it out of work!
The Outlook shared calendars work quite well – we use them for general knowing-where-people-are purposes, and also for planning leave, to try and make sure there aren’t too many people off at the same time. Busy periods of term are highlighted, so we know there is a very limited number of people who can be on leave during these times.
I used to use a paper diary for work, when I had to create rotas, mainly because we didn’t have the shared leave calendar at that point and I needed somewhere I could record when people were away, as well as when pool staff were coming in. It was also useful to have a paper diary to take with me to meetings and so on. I don’t have to create rotas anymore, and I don’t go to very many meetings either, so I’ve given up using a paper diary for work, although I still have one for non-work things.