The idea of using a source calendar and then other calendars to stack on top of the initial one is just brilliant!
Gives you, more or less, a limitless amount of calendars (Events, Holidays, Weather, Birthdays, et cetera) to display ... all one 1 calendar! Allows the viewers to toggle the calendars on and off in the top right corner. This really takes advantage of what Google intended their calendar system to be. This, coupled with GCalendar is great too! The calendars show up in GCalendar and then you could use the "Upcoming Events" module from calendar to pick and choose which calendar it's going to display for.

This is a must have. Simple to setup ... may take a 5 minute learning curve if you don't do it correctly the first time (Setup a bunch of "Sources" first THEEEEEEEN a calendar) In the end, you should have 1 calendar and then multiple sources to display on the calendar.

I've had waaaaay too much coffee this morning, so I'll stop there. Hats off to the development here!