I use Settings | Applications | Manage Applications | Calendar Storage | Clear Data and it goes through the motions, asks if I'm sure and shows 0 bytes as the new numbers but the calendar entries are still there. When I repeat the steps, it shows the true memory (not 0) being used. The same procedure works fine to clear contacts. Update / Problem Solved -- I deleted all entries in my Google Calendar and the problem went away. Apparently, as soon as I deleted the calendar data, it was replaced from the Cloud. The lesson for me is: if your going to sync with Outlook, you can't use Google Calendar.