Visual Studio 2008 SP1 is packed with new features, major updates to frameworks, and fixes. So much so that with everything installed (including x64 and ia86 support) you would need to download and install about 1GB of updates. Which brings us to the first and most important performance improvement – you only download what you need!
VS2008 SP1 includes a new installation / update engine. You just download the installer, which then analyzes your system installation, and only downloads the components you need.