Microsoft has provided little in the way of guidance as to when a product should adopt or switch to WPF. Recently, Microsoft published a whitepaper with a small amount of guidance here, entitled "Deciding When to Adopt Windows Presentation Foundation." The whitepaper describes mostly technology choices and integration options. If you're not familiar with WPF and it's integration options at a high level, the whitepaper is worth a read. I'd suggest it might be good for a technical manager who's new to WPF. If you've gotten your hands dirty in WPF though -- it won't be very enlightening.

If you're just interested in the final conclusion, I've snipped that section and put it here:

In conclusion:

• If you have an existing Windows Forms application or are building a traditional forms-based application and are looking for a mature technology to use with mature tools and component support then Windows Forms is a good fit.
• If you have an existing Windows Forms (or MFC/Win32) application that could benefit from some of the advanced presentation features of WPF, you can add WPF to your existing project.
• If you’re wanting to create a new experience for your users that is rich, interactive, sophisticated, or highly custom or branded, WPF is Microsoft’s next-generation platform for your project today.
• If you’re targeting the web, Silverlight shares the same development model as WPF but is optimized for a lightweight, cross-platform runtime. Investing in either WPF or Silverlight nets you the skills, tools, and assets for both platforms.

With all of these choices, you can be assured that all of these platforms will be supported for years to come.

The MFC/Win32 application that isn't using managed code today has the most at risk -- as the application would require a large additional framework installation.