Win 7 SP1 adds two new features and tons of bug fixes.
After releasing it first to its MSDN/TechNet subscribers, Microsoft has now made the first service for Windows 7 public.
Among the myriad of bug fixes and performance improvements, the Win 7 Sp1 will introduce two features.The first of the two is RemoteFX, a remote desktop software for Windows Server 2008 R2 that allows users to watch high-quality video and interact with 3D applications. The second one is HyperV which dynamically adjusts RAM requirements between virtual machines to provide optimum performance for heavy tasks.
You can read more about the update here. The SP1 will be automatically be installed if you have Windows Update turned on.