Microsoft recently announced there updated cloud service named Office 365.
Office 365 includes Sharepoint 2010 online and there are some information available for developers that describes what possibilities there will be for building solutions on top of Office 365.
Office 365 includes Microsoft Exchange, Sharepoint 2010 and Lync.
Look’s like there will be good opportunities to customize and develop solutions for Sharepoint online in Office 365. Microsoft have a article describing the process for customizing Sharepoint online here.
The article includes this table describing the differences between Sharepoint Online and Sharepoint installed in-house. Click the picture to see the table.