Official Google Enterprise Blog: Serena Software on switching from Microsoft Exchange to Google Apps

"The overall move to Google Apps took all of six hours. We waited for the phones to ring, but all we heard was silence – in fact, we sat there playing meebo for quite a while – and still, nothing happened. We cut the cord all in one stroke to avoid the hassle of living in two environments at once. We made the switch globally, all in one day – and, due to the advantages of this cloud computing solution, we’ve never looked back."