*Update*

The issues have been resolved.

Microsoft has confirmed restoration of OneDrive for Business/SharePoint Online services.
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Previous Description (2016-04-25 14:56:43):

Individuals using SharePoint Online features, including OneDrive for Business, through the web interface may experience reduced functionality and/or receive messages indicating that the server is busy and to try again later.

Microsoft is currently investigating the issue. ITS will post an update to this notification when services have been restored.