During the SharePoint Conference in Las Vegas last month, attendees were introduced to the new Office 365 APIs. Today, some of those API were released into preview for Visual Studio, as was announced on the Apps for Office and SharePoint Blog. Only some of the APIs were made available such as the mail, calendar and contact REST APIs and then only for C# and VB.net apps.
There are some good sessions on the APIs from the March 2nd - 6th SharePoint Conference in Las Vegas, NV. If you are thinking of trying out the new APIs then you should definitely go over to Channel 9 and check them out. Also below is the link for the preliminary/preview documentation for the APIs over on MSDN.
Link for the MSDN API info: