Just to add to this, even Special Notices are not sent out immediately for those who are using a digest or summary. If you need to send everyone a message right away you'll either have to do that through the Actions->Send Message pull-down from the Members tab, or download your member list into a spreadsheet and paste the addresses into your email client.
I also don't believe there is currently such a thing as a true Google calendar integration; meaning the ability to import calendar entries from Google into GIO. It has been requested in beta and I would dearly love to have it.
Bruce
Bruce