I’m impressed with the list of improvements sp1 brings to Vista. My system is much more stable overall, and more responsive overall.  Some things worth knowing about SP1 are:

• Windows Vista SP1 includes a new compression algorithm for the RDP (Remote Desktop Protocol) that helps reduce network bandwidth required to send bitmaps or images via RDP. The compression, which can be selected by administrators via Group Policy settings, is transparent to all RDP traffic, and typically reduces the size of the RDP stream by as much as 25-60%, based on preliminary test results.
• Adds support for Direct3D® 10.1, an update to Direct3D 10 that extends the API to support new hardware features, enabling 3D application and game developers to make more complete and efficient use of the upcoming generations of graphics hardware.
• Adds support for exFAT, a new file system supporting larger overall capacity and larger files, which will be used in Flash memory storage and consumer devices.
• Improves performance over Windows Vista’s current performance across the following scenarios:
• 25% faster when copying files locally on the same disk on the same machine 
• 45% faster when copying files from a remote non-Windows Vista system to a SP1 system
• 50% faster when copying files from a remote SP1 system to a local SP1 system 
• The Windows Vista SP1 install process clears the user-specific data that is used by Windows to optimize performance, which may make the system feel less responsive immediately after install.  As the customer uses their SP1 PC, the system will be retrained over the course of a few hours or days and will return to the previous level of responsiveness. 
• Windows Vista SP1 includes a new Security Policy (UAC: Allow UAccess), which allows applications to prompt for elevation without using the secure desktop.  This allows a remote helper to enter administrative credentials during a Remote Assistance session
• Allows users to rename or delete folders while working offline with redirected folders. This functionality is important to users that use Folder Redirection and work in offline mode for extended periods of time. This functionality is disabled by default but can be enabled by enabling a registry setting. 
• Adds a WMI interface as a replacement for the MoveUser.exe tool which was removed from Windows Vista.  This allows customers to remap an existing workgroup or domain user account profile to a new domain user account profile.
• Enables support for hotpatching, a reboot-reduction servicing technology designed to maximize uptime. It works by allowing Windows components to be updated (or “patched”) while they are still in use by a running process. Hotpatch-enabled update packages are installed via the same methods as traditional update packages, and will not trigger a system reboot.
• Improves OS deployment by enabling 64-bit versions of Windows Vista to be installed from a 32-bit OS.  This will allow IT professionals to maintain just a single WinPE image.
• GPMC (Group Policy Management Console) will be uninstalled with Service Pack 1 and GPEdit will default to Local Group Policy editing. Following these changes, SP1 users can download an updated version of GPMC which will include new Group Policy capabilities including adding comments to GPOs or individual settings and searching for specific Group Policy settings.
• SP1 reduces the number of UAC (User Account Control) prompts from 4 to 1 when creating or renaming a folder at a protected location

Again, see all the changes here: http://download.microsoft.com/download/f/4/a/f4a35b2b-2f62-4104-a3e6-5f7bc1318e9f/Notable%20changes%20in%20Windows%20Vista%20SP1.xps