One major shift from SharePoint on-premise to SharePoint via Office 365 from an Administrators point of view is that you now don’t get a chance to test/evaluate enhancements and the impact they will have on your users / applications that you have built on top of SharePoint. With SharePoint on-premise you could always apply the SharePoint Cumulative Update or Service Pack in a test environment and check that all your applications/customisation still work and identify any areas that you may need to train users or modify business processes to ensure a smooth upgrade.
Enter Office 365 and SharePoint online.
You now don’t get a chance to see and test the changes/enhancements until they appear on your live site. This could leave you doing a mad scramble to ensure your applications and users can continue to work smoothly.
Microsoft have launched a Wiki site dedicated to keeping the public informed of upcoming enhancements and changes to both the Enterprise and Professional Office 365 plans. While this is still a long way from providing the public with a “test” version of their Office 365 environment with the update applied, it is a solid step in the right direction.
http://community.office365.com/en-us/w/office_365_service_updates/default.aspx
Cameron Dwyer 
I just came across this on Tony Redman’s blog:
http://thoughtsofanidlemind.wordpress.com/2012/05/02/tec2012/
It seems Microsoft have acknowledged the issue of updates in the Microsoft cloud environment with customers having little ability to control the impact until after it has happened and are starting to address it at a technical level. In this particular case the reference is to Exhange Online.
“Exchange Online follows a cadence of three-month, six-month, and annual updates to keep the service fully patched and as up-to-date with features as possible. When new features are introduced, everyone gets them at the same time. Some customers have difficulty with this aspect of the service. For example, if a new version of OWA is introduced it can have downstream consequences for on-site user support. Microsoft is figuring out how to allow customers to have greater choice and control over when (but not if) new features are deployed to their users.”
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