If you use iCloud with your iCal, be VERY CAREFUL! If you stop using iCloud, you will lose ALL of your calendars, even if they were orginally on your Mac. It's as if once you use iCloud, your data is sent to Apple, then that data is erased from your Mac. Other than a warning that the data will be deleted from iCloud, there is nothing warning you that ALL of your data will be gone. No options! No settings! No warnings!
I stopped using iCloud within a few days of starting it. It ruthlessly abducted 99% of my internet bandwidth for its updates; everything slowed to a crawl; browsing simple websites took 15 minutes to download... EACH! I thought I had a virus until I noticed my router going crazy (as well as my network seen in Activity Monitor). It was as if I had a virus. Finally, I realized this all started when I activated iCloud. To test my theory, I shut down iCloud, thinking it was no big deal. It fixed my network problem, but totally erased ALL of my calendars, schedules and appointments.
I have no idea if my thousands of Aperture photos, Pages documents (legal contracts), Keynote presentations, etc., years of data, would be gone if I were to have uploaded them, too.
After the constant 3.7-year (avg) cycle of losing my data, emails addresses, etc. to a new Apple "improvement"...
iTools 2000 - 2002 (2yrs)
.Mac 2002-2008 (6yrs)
MobileMe 2008-2011 (3yrs)
iCloud 2011-Present (???yrs, 2011+3.7 avg = 2014 end of life?!)
...I have finished trusting Apple with my data! Apple isn't building "data farms" and servers, they are building immense data incinerators.