It's not really SP1, it is a hotfix rollup that addresses a number of issues in Visual Studio 2008. It can be downloaded from here.

Check the installation instructions, particularly if you are running on Vista with UAC enabled, here.

The issues addressed in this hotfix include:

HTML Source view performance

• Source editor freezes for a few seconds when typing in a page with a custom control that has more than two levels of sub-properties.
• “View Code” right-click context menu command takes a long time to appear with web application projects.
• Visual Studio has very slow behavior when opening large HTML documents.
• Visual Studio has responsiveness issues when working with big HTML files with certain markup.
• The Tab/Shift-Tab (Indent/Un-indent) operation is slow with large HTML selections.

Design view performance

• Slow typing in design view with certain page markup configurations.

HTML editing

• Quotes are not inserted after Class or CssClass attribute even when the option is enabled.
• Visual Studio crashes when ServiceReference element points back to the current web page.

JavaScript editing

• When opening a JavaScript file, colonization of the client script is sometimes delayed several seconds.
• JavaScript Intellisense does not work if an empty string property is encountered before the current line of editing.

Web Site build performance

• Build is very slow when Bin folder contains large number of assemblies and .refresh files with web-site projects.

Cheers,

Robert Porter