The first service pack for Windows 7 and Windows Server 2008 R2 will only contain minor updates, and will not include a lot of new features. The server variant of the service pack will introduce RemoteFX and Dynamic Memory.
"With Microsoft RemoteFX, users will be able to work remotely in a Windows Aero desktop environment, watch full-motion video, enjoy Silverlight animations, and run 3D applications," Microsoft's Max Herrmann writes, "All with the fidelity of a local-like performance when connecting over the LAN."
Dynamic Memory is an improvement to Hyper-V which allows users to pool all available physical host memory together, and dynamically allocate it to virtual machines. In other words, if the workload changes, VMs can get access to extra memory without having to shut them down.
Client-side, the service pack delivers mostly bug fixes and the like, as well as the client aspect of RemoteFX, updating Remote Desktop to take advantage of said new technology. As usual, both client and server versions will also include all updates released up until that point.
As said, no release schedule has been announced.