The early adopters' curse...
We have been a Google Apps for Education school since May 2006 - but we have been using Google Calendars for our school calendars well before then.
These were on private Gmail accounts, and as such could not be used with our Apps Groups system - so we decided to import these calendars to our "dash net" system (what we call Google Apps).
We set up a new calendar using a dummy user and then each calendar (Primary, Secondary and Whole School).
Exporting from the original Gmail calendars was easy. From Calendar Settings on the drop down arrow of the calendar, you press the ICAL button on the calendar address. Pressing the OK downloads a basic.ics file. This is the one you then import into the Apps calendar that you have prepared.
It was a smooth process.
a) keep the basic.ics file from each calendar - you then have a back-up if things go wrong;
b) restrict the old calendars to private view so that they then do not appear - there does seem to be some time lag, however, since we had some unexplainable appearances of the old calendar;
c) name your new calendar DIFFERENTLY so that you can recognise the new one from the old one, if things do not work out well (see b);
d) share using the Groups system - first signs are that the clicking on the link added the calendar - do remember that you will probably get threaded messages from your dummy user account notifying you of the new calendar and you may have to "show text" to be able to see it;
e) Macs - there seem to be some problems here - investigating these but first comments are that it was easier to add by url.
You would have thought that it would be easy to find a group calendar. Not a bit. A plea to Google - please make it easier to find group calendars within a domain! Perhaps a tab on Browse Interesting Calendars listing all the group calendars shared within the domain?
Okay - calendars out of the way, blogs next when these become part of Google Apps....