Service Pack 1 has been announced publicly http://msexchangeteam.com/archive/2010/04/07/454533.aspx with a public Beta expected in June before the release later in the year.
In the 6 months since release of Exchange 2010 the MS Exchange Team have continued to work on those features that didn't make the cut for the RTM version, or needed some improvement based on feedback from deployments in the wild and from the close technology adoption programmes.
- There's LOADS of work been done on archiving – flexibility around personal archive stores, PST import, delegate access; and lots of work on eDiscovery including improvements to multi-mailbox searching
- OWA, which was already really good in 2010, is now faster with a more instant feel. It does feel more like the Outlook experience now, especially if you're a busy with your mouse in your mailbox and like to read/delete/move in a flash. OWA did drag a bit when you got busy.
- For admins, there's added support in the EMC and ECP for some of those 2010 features that you previously could only manage with Powershell – Journal rules, mailtips, RBAC roles etc.
For more info on Addressing E-mail Archiving and Discovery with Microsoft Exchange Server 2010, there's a brand new white paper (which includes the updated SP1 features) by Ian Hameroff here: http://download.microsoft.com/download/4/3/A/43ABF6CF-B8FE-45B3-9196-21B1F0C52E43/E2010-Archiving-WhitePaper.docx