Felix Huang, a developer on the Visual C++ team just posted a great blog post entitled
VC MSBuild Extensibility Example. His post shows some of the cool build extensibility features coming to Visual Studio 2010. I definitely can think of uses for this type of thing in the builds I work on. I wonder what other additional things you can add.
Hopefully it will support conditionally choosing which certificate to sign your code with based on whether its an official release or a dev build. This might require calling a different executable, etc. I'm hoping all of this is covered. Right now my builds do this as part of the build scripts after the VS Solution is finished compiling.