Microsoft have revealed plans for Exchange 2010 service pack 1. The beta version will be available at the end of June. It will contain all previous rollups and also some new enhancements including:
Archiving and discovery enhancements
Outlook Web App (OWA) enhancements
Mobile user and management improvements
Added UI for management tasksAnd the PST file management will have some [...]

Exchange Server 2007 SP2 features.