What are some convincing arguments to upgrade from Visual Studio 6?

Question

I have a client who is still using Visual Studio 6 for building production systems. They write multi-threaded systems that use STL and run on mutli-processor machines.

Answer 1

Not compatible with Vista. Heck, there's a long list of issues VS 2005 has with Vista.

That being said, most of the improvements in VS seem to apply to everything other than C++ native code. What I'm seeing is more standards compliance, which is important but hardly dramatic.