- Coexistence with Exchange 2013. This SP is required before you add Exchange 2013 to an existing Exchange 2010 organization. However, you also need cumulative update 1 for Exchange 2013 which has not been released as of today (Feb 13, 2013). Exchange 2013 CU1 is scheduled for release sometime in Q1 of 2013.
- Support for Windows Server 2012. Without this SP, you cannot install Exchange 2010 on a computer running Windows Server 2012.
- Support for IE 10 in OWA. I've not tested it, but without the SP apparently OWA does not work properly with IE 10.
A Technet blog announcing the release is here: