When you first launch BusyCal, all of your iCal data is instantly imported. The data is actually imported from Sync Services and/or iCloud — the underlying technologies on Mac OS X for syncing calendar data between iCal and other apps/services like BusyCal.
Since BusyCal syncs with iCal through Sync Services and iCloud, any changes you make to your calendars in BusyCal will continue to be synced with iCal. If you later decide not to use BusyCal, all of your data will be current in iCal.
If you wish to stop using BusyCal as your primary calendar and switch back to iCal, you should reset BusyCal. To reset BusyCal, launch BusyCal and select Help > Reset > Reset BusyCal. BusyCal will clear its publish and subscribe settings, delete its database, set iCal as your default calendar application, and quit.
You can sync calendars on your LAN between a mix of computers running BusyCal and BusySync.
You cannot run BusySync and BusyCal simultaneously on the same computer. If you are running BusySync when you launch BusyCal, a confirmation dialog will appear informing you that your BusySync data will be converted to BusyCal and BusySync will be stopped.
If you attempt to start BusySync after running BusyCal, a dialog will ask you if you wish to convert your BusyCal database to BusySync format. BusyCal must be installed in order to perform the database conversion. Once you convert the database, you will be able to start BusySync.