How to opt-out of "Today Calendar" and not be displayed in anyone's calendar
If you do not want to be added in calendars your friends make using this application, you can do the following:
1) Install the application – even if you don’t use it, you’ll remove it at the last step. Install it here: http://apps.facebook.com/todaycal
2) Choose “Settings”
3) Uncheck the last option “Include me in calendars created by me and my friends”.
4) Now uninstall the application. You can do this here: http://www.facebook.com/settings/?tab=applications
Find the application “Today Calendar” and click the “X”. We will delete all information, except of course your choice to never be included in calendars your friends make.