ASPNET_MERGE and Web Deployment Projects Arrive!
And Brian Goldfarb's blog item with additional links is here
"Visual Studio 2005 Web Deployment Projects provide additional functionality for building and deploying Web site applications that you create in ASP.NET 2.0 and Visual Studio 2005. This add-in includes a new tool that enables you to merge the assemblies created during ASP.NET 2.0 precompilation, and it provides a comprehensive UI within Visual Studio 2005 for managing build configurations, merging, and pre-build and post-build task using MSBuild."
... And the good news: IT REALLY WORKS!