Practically old news now but:
· If you previously installed a Visual Studio 2008 Hotfix, you must run the Hotfix Cleanup Utility before installing Visual Studio 2008 SP1. For more information, see Visual Studio 2008 Hotfix Cleanup Utility for Installing Visual Studio 2008 SP1.
· If you have multiple Visual Studio products installed, you must upgrade all of them to SP1. If you have Visual Studio 2008 and one or more 2008 Express Editions, you cannot upgrade the Express Editions until you have upgraded Visual Studio.
· Prior to installation, you should carefully review the included readme file to be aware of any known issues with this release.
For feedback on the Service Pack, please visit https://connect.microsoft.com/VisualStudio