<p>I understand that there are several ways to blend XNA and WPF within the same application. I find it enticing to use WPF for all GUI and HUD stuff in my XNA games. Does anyone have any practical experience on how well this approach works in real life using .NET 3.5 SP1 ? Any pitfalls (such as the <a href="http://blogs.msdn.com/nickkramer/archive/2005/07/14/438640.aspx" rel="nofollow noreferrer">"airspace problem"</a>)? Any hint on what appoach works best?</p>

There is an addition in 3.5 SP1 that allows better interaction between DirectX and WPF (D3DImage), and one way to get to that is through XNA.
Here are some details:
http://jmorrill.hjtcentral.com/Default.aspx?tabid=428&EntryID=259