In an attempt to be more responsive, Microsoft is trying to publicly release hot-fixes more frequently. This hot fix affects the performance of VS 2008 when editing web pages.
Areas of improvement include HTML source view, design view, HTML editing, JavaScript editing, and web site build performance. For a complete list of improvements, see Scott Guthrie's blog.
Scott is also soliciting feedback from developers still having performance problems after installing the service pack.
Can you send me an email (scottgu@microsoft.com) with more details and I'll loop someone on the team to investigate? Can you as part of that email also bring up the VS 2008 about box and use the "Copy Info" button to paste your current VS configuration in the email? That will help us identify whether you have the patch installed correctly, and/or what your VS configuration looks like (and if you have any 3rd party VS plug-ins installed that might cause problems).
Buried deep in the comments Scott also mentioned VBScript. Though considered obsolete for over half a decade, many sites still use a mix of classic ASP/VBScript and ASP.NET. Scott writes,
We are going to enable VBScript intellisense support with the next roll-up patch/SP. We have this working now - just need to finish testing it.