There seems to be some kind of (hopefully temporary) problem at the Google's calendar as it doesn't return any events for the other calendars. No idea what is causing it or when it gets fixed.
I'm having the same problem, subscribing to the "Contacts' birthdays and events" calendar used to be working to make the contacts' birthdays show up in Rainlendar, but since a week or so it's not working anymore. Maybe clients must now explicitly use GData API v3.0 as suggested by the thread at ?
PS: Other special calendars like "German Holidays" seems to be broken, too.