This is a must have hotfix.

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, colorization 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.
• JavaScript IntelliSense does not work when jQuery is used.

Web Site build performance

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

Source:
http://weblogs.asp.net/scottgu/archive/2008/02/08/vs-2008-web-development-hot-fix-roll-up-available.aspx