A common misconception about Office 365 is that existing customers get upgraded immediately. That is not the case. New customers get access to the new product at launch time. Existing customers need to have their service upgraded by Microsoft. As you can imagine, there must be many petabytes of data to shove about during these upgrades and it happens gradually. While the BPOS to Office 365 upgrade was extremely complex (BPOS was based on Office products that were not designed for the cloud) it appears that this 2013 upgrade will be much smoother and quicker.
The admins of our Office 365 account at work just got this notification:
If we wanted to test this upgrade to check for negative impacts:
In about 4 weeks, your organization will receive an upgrade to your Office 365 service. You can experience the service upgrade with a small group of users immediately.
Note that the admin appears to get a customer-specific link for the test.
And if you want to delay the upgrade:
If you really need to, you can postpone the service upgrade right from the Admin page.