I'm currently a two calendar person. For my academic advising position at OSU, I utilize Outlook as my primary calendar. Advising appointments are placed on my calendar throughout the day. During peak advising, it's not unusual for my calendar to have 12 advising appointments on it for every day of the work week. Outlook tells me where I am supposed to be at every hour of the work day.
My other calendar is Google Calendar . I use it to keep track of my consulting endeavors, birthdays, and other life events. While it's not perfect, Google Calendar has been my go-to calendar for quite a while. The nice thing about my current calendar situation is that I can sync my Outlook and Google Calendar entries on my Droid X smartphone. Before I purchased the Droid X, I would have to check back and forth between my calendars. I could have synced Outlook with Google Calendar, but due to the variability between both calendars and their distinct uses, I decided to keep them apart from each other.
One of the biggest challenges to having 2 calendars (trust me, I know that some of you are laughing about this as you have more than 2 calendars to manage) is scheduling meetings amongst groups of people. Simply sharing calendars is not enough. I often block out time on my calendar that isn't necessarily "booked," I just need time throughout the day for miscellaneous tasks. Someone viewing my shared calendar in Outlook can't distinguish between a "hold" versus a real meeting. My favorite way to schedule meetings with folks has been via Doodle . Doodle simplifies the process of scheduling a meeting. It breaks down the difficulties of multiple people struggling to find an available day and time. If you are not using Doodle, take my advice, it will make you very happy.
In addition to Doodle, I have also looked into exploring Tungle.me  as a way of sharing my calendar and making appointments. It looks like it might be a bit more advanced than Doodle. However, Tungle.me's feature set could come in handy for a lot of folks who need to manage their calendar in a team environment . The neat thing about Doodle and Tungle.me is that they connect seamlessly with Google Calendar. Very nifty.
In the near future, my calendar situation will become much simpler. My last day at OSU is approaching quickly. In October, I will rely solely on Google Calendar to organize my consulting schedule. I will finally have "one calendar to rule them all."
How do you manage your calendar(s)?
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