Channel 9 (the Microsoft MSDN tech channel) showed a video on interactive 2D controls on WPF (Windows Presentation Foundation) surfaces. There is also a new blog on this topic.
Maybe this feature of WPF will soon be highlighted as the best thing since sliced bread - but Squeak Smalltalk had some of these features since years. Maybe you remember the bunny demo where you can easily mix 2D and 3D in Smalltalk.
Have a look at Croquet - there you can easily use 2D morphic projects and mix them with interactive 3D scenes. You can select 2D objects in 3D, interactively change them and even type and select text.
And it's based on Smalltalk - therefore it is platform independent and completely open source ...