While building my 3D Animation tool[1] I used a lot of ScreenSpaceLines3D[2]. Unfortunately Microsoft decided to remove them from WPF release 1[3] After complaining (begging even) Dan Lehenbauer[4] responded and today he released a new build of his ScreenSpaceLines3D[5].
The good news is that these new SSL3D class can replace the old SSL3D in many situations. The bad news (for me) is that the new SSL3D class does not inherit from Model3D so it's pretty tricky to have several new SSL3D share the same data (data binding). I am creating a wrapper thingy that will allow me to do just that.