I am an experimenting with a Silverlight port of a WPF control, and find all kinds of funny things about Silverlight.
The good news is that Silverlight team seems to pay a lot of attention to performance. I have an animation of a dozen or so visuals: same code shared by WPF and Silverlight project. WPF animation works fine on a modern machine, but staggers hopelessly on older computer (3.2GHz Pentium 4, Matrox Millenium G450 video card). Silverlight animation works great on the same old computer.
It’s too bad Silverlight is dead and being replaced with WinRT 🙁