Here is a great case study on an all-Mac shop moving their email and groupware solution over to Google Apps:

Just a reminder, if you are looking to do this, Mac or otherwise, we can help with our Google Apps Setup Service.

And while we are talking about Macs, Mac )X X 10.5.3 update has slipped in Address Book <-> Google Contacts synchronization using the iSync subsystem. This also enables, it appears, iCal to sync with Google calendar as well. Learn more about it here: mac-os-x-1053-sync-google-conta