While reading the “Whidbey” roadmap, I found this:

MSBuild will be completely transparent with regards to how it processes and builds software. All build steps will be explicitly expressed in the XML project file regardless of whether it was authored by hand or auto-generated by the Visual Studio Whidbey IDE. This also means that Visual Studio no longer treats any part of the "F5" build experience as a black box. A user can now understand, replicate, edit, remove, or augment any part of the build process.

Sweet.  NAnt-like functionality with Visual Studio ease-of-use.